There is lots of information available on these horns, and many consider them some of the best horns ever made. However, there are quite a few variations of the transitional horns. It is generally agreed they start at the 235,xxx serial and end at the 260,xxx serial number. I'll try to give a rough and general overview for you.
There are a number of features that designate a "transitional" model Conn saxophone from the early 1930's. These include the raised side High E key, the swivel thumbhook, the G# pinky cluster arrangement, the split vs. same side bell keys, engraving style, and the neck arrangement.
The first iteration had the raised side High E key, seen in this picture here.
http://www.saxpics.com/?v=gal&a=967 These very first "transitional" altos will sometimes have the "Chu Berry/New Wonder II" standard engraving, or some later ones might have the "Art Deco" style engraving seen in the link. These are purported to have the same body/bore as a Chu Berry/New Wonder II model and, in my experience, play very similarly to the Chu Berry models. Most of these seem to have the standard "Chu Berry" neck with the overslung octave mechanism.
Another iteration is the first introduction of the "same-side bell keys" that can be found starting in the 240,xxx range, but it is possible to find one earlier than that. You can see an example of this at this link:
http://www.saxpics.com/?v=gal&a=943 Notice how the G# pinky key is smoothed out and no longer has the "Nail-file" look of the earlier models. These will typically have the Art-Deco style of engraving but it is possible for them to have other engraving, such as the standard 6M "Naked Lady" engraving. I have seen these models have both the overslung model neck as well as the underslung neck. It is also possible to have "split bell keys" with the underslung neck and art deco engraving.
The last iteration is pretty much a 6M in almost all respects, save for the swivel thumbhook. The left hand pinky table is of the 6M design, the engraving is typically the full "Naked Lady" 6M engraving,and it is the 6M underslung neck. The swivel thumbhook (sometimes called "the transitional thumbhook" by people) is the only difference between these late Transitional models and the early true 6M's that follow. You typically start to see these in the 250,xxx range. You can see pictures at this link:
http://www.saxpics.com/?v=gal&a=954
There are of course variations to this. The 240,xxx to 250,xxx range is where you might see the most variability.
As far as playing, the earlier models have a bigger overall presence and are a bit more spread to me. The later models have slightly more focus, sound a little more refined, and have better intonation. That being said, all vintage Conns from around 1930 can be excellent players when set up properly.
Whether or not it will work for you is something you'll have to decide. If you already have an alto you like, I wouldn't advise selling it on a whim for something you've never tried before. Try to get to a music store or sax shop that has one of these available to test play. Then you can decide if you like the general character of the horn and make an educated decision.
My opinion is the 250,xx range are the best playing of the horns. I have played quite a few in this range, and when properly set up they are absolute magic horns. Just my opinion. As far as value, these can be all over the place. Mostly it depends on condition. A relacquered one that needs pads will be less than $1,000 whereas a full rare gold plated one can exceed $5,000.....most of them tend to be in silver and can go for $1300-$2500 depending on condition and playability.
Best of luck and hope this helps!
- Saxaholic
