I have owned a Selmer low A baritone from the Mark VI era, and I currently am playing a Yamaha YBS 62 horn that I acquired used back in 1986 or so. And, I have played a wide variety of baritones as well, save only the odd brands (Couf and the like).
Having been impressed by my Conn artist level model alto that I had rehabbed back in the early years of this decade, I have been on the lookout for a Conn baritone from the same era for many years now. Sad to say, I have yet to find one.
I will readily admit that the sound that you can draw from a well set up classic Conn horn is without compare. It has more "roundness", more "belly", more presence, and more volume with less effort that do other horns commonly played. (In this respect, it is apparently joined by those from the Martin firm; I've only played one so I don't qualify as a competent judge there.)
There are various reasons why this is so, but I can't say which one it is. I do notice that the vertical portion of the sax going down to the bow upon which the bell is mounted is not circular in cross-section, but rather oval or "D" shaped.
I go so far as to call the Conn sound the "American" sound, as contrasted with the "French" sound of most others. The first time you ripple through a chromatic scale on one, you will almost certainly say "Wow!".
That's the good side. Now, let's look at the bad side.
There are several problems that mitigate against acquiring one, at least from my point of view.
• KEYWORK
First and foremost, the keywork on the 'old' Conns is horrible with a capital H. It's not fast like on a Selmer horn, and many of the mechanisms that the good colonel used are not as responsive as those used by a "French" style horn. While this is a minor inconvenience on the alto and tenors so prized by aficionados, on the baritone and bass horns it is a major negative.
I'm not just talking about the problems with the left hand little finger here, although they are major enough to scotch a sale on their own for many players. The good colonel or his agent must have envisioned his saxophones for members of the ape family, for you have to reach, twist and apply pressure that works 'sideways' on the thumb hook thumb in order to make them work.
I have quite large hands, and have well developed muscle groups operating them as well (years of working as a bricklayer and playing ice hockey tend to do that to your hands). While I can exert enough force with my little finger to operate the left hand little finger keys, it is not a pleasant experience. Unlike all of the other "finger moves" on a horn, you are not pushing down but also sideways. (The palm keys function this way, but they are well spaced out, not concentrated in a three-quarter inch square area.) If you have the slightest bit of problem operating that LH little finger cluster on any other baritone, then steer well clear of the Conns.
There is no such thing as a graceful move from low B to low C# on a traditional Conn horn, no matter how good your technique may happen to be. It's not a matter of the player, it's a matter of how physics allows you to apply force to the keywork.
Incidentally, this is not exclusive to Conn instruments. On my Oehler clarinet (German style system), the "long key" for the F#/C# is operated in a similar fashion. It is quite cumbersome to use, and I usually use the "patent C#" mechanism for almost all moves to those notes.
However, in addition to the LH little finger problem, everything else on the horn is spaced out in a "funky" fashion to one accustomed to saxophones based largely on the Selmer designs. On alto or tenor, this is not a major problem, although irritating to some. On the baritone or bass, it is much more obvious.
(Just yesterday, I played two performances of Crazy For You, and the baritone part in that show involves a lot of movement from low C# to other low notes (including low A). Often I will practice a new baritone part on my Conn alto when working up such a job, just to get the fingerings figured out without hauling out the big horn. But, whenever the low end figures prominently in music, I know that it is futile to bother with the Conn system of little finger keys. Had I been using a Conn baritone, the fast moves(quavers and semiquaver) from C# to other notes in the vicinity just would have been impossible (never mind the low As).
• OVERALL LAYOUT
The second issue that would mitigate against going the Conn route (for most sax players is the overall arrangement of the horn. The factory original thumb hook is a device of torture, plain and simple. The Conn baritones that I've tried (all from the "good old days", one of them equipped with a finish straight out of a Rustoleum spray can) don't seem to balance as well as the newer horns. Both of these problems can be fixed, but they do require a little more than minor work by a repair technician.
• MOUTHPIECE ISSUES
The third factor against the classic Conn instruments is the mouthpiece that you may be using. On my alto, things just did not tune or sound right until I got myself a stubby rubber mouthpiece. My choice of a Berg Larsen for my normal playing setup just would not work on a Conn alto.
(This might be a part of the reason why the Conn baritones that I've tried were not barn-burners, but I had no such problems with the altos that I've used them on (just with the tuning). So, you may have to change your "setup" if you go the vintage Conn route.)
• THE STINK FACTOR
Next, they all seem to stink. The horrid, left in a damp climate and moldering for thirty years stink. Even if you get a Conn saxophone stripped down to bare metal and have it re-plated, with all new "non-metal" items like pads and corks and felts, there is still a little of the residual smell present. Not a deal killer for many, but I've known many people who wouldn't go near a moldy horn. If you're one of these, then pass the old horns by.
• PRICING CONCERNS
The next factor has little to do with musicianship and a lot to do with your pocketbook. There's no denying that saxophone are expensive items. However, they are comparatively expensive as well.
An alto horn may set you back a thousand or so (talking about a Conn in superb playing condition, but see below). A tenor will set you back proportionately more, particularly as these horns are sought by jazz folks who will trade just about anything for the sound that they give out. However, the baritone of the species (assuming superb playing condition) starts to drive the price point off the charts.
I have play tested every Conn baritone that I have been able to get my grubby hands on. Of these, all but one was in playable condition. (However, had I made the purchase, I would had them completely overhauled and refinished (and would have burnt the cases toute suite). Those that were playable had prices approaching a used YBS-52 in ready to run condition. And, all but one of them came with a case that stank to high heaven.
So, if I had taken the plunge on any of these horns, I would have been out at least three thousand dollars, and maybe more depending on the level of rebuild. While I can afford that kind of tin, most cannot. And, if you had to borrow your previous horn (from what appears to be a United Kingdom "city" or "county government", if I understand it correctly) you too are probably not in the position to "take a plunge" on something that is almost certainly a "work in progress" when you purchase it.
While the Conn sound is something that every saxophone player needs to know about and experience even if only once on a borrowed horn, it comes with a lot of negatives. Only you, of course, will know if the positives outweigh the negatives. For almost everyone on the planet, I would say that they don't.