Mixing up the terms 'tipped-bell' and 'saxello' is counter-productive. The modern 'tipped-bell' sopranos are actually copies of the Buescher Tipped-Bell soprano. I think they're the best answer for the casual soprano player. Its much easier to get a mellow sound out of them than a straight.
But to the question, the saxellos I have heard including King Curtis's Martin 'American' seem to be a little treacherous on intonation. Did they not have the full-curved soprano at that time? That would seem to take care of the prime reason for the saxello of being able to project forward without holding it straight out like a regular soprano.
Well, I think different companies had different reasons for making sopranos in between the totally straight and the fully curved (like a little bitty alto shape). For the American companies I have really only seen Conn and Buescher curved sopranos and their stencils - there are also some "Yorks" floating around that might or might not be stencils from someone.
So as far as I know King, Martin, Selmer never made curved sopranos (if memory serves there might be a tiny number of Selmer curvies). It seems then that King made the true Saxello, maybe so they could have something that wasn't the straight, and without paying one of their direct competitors for a stencil curved. I think Martin may have stenciled some of those weird semi-curved Lyon/Healy/Couturier sopranos?
I don't recall ever reading about a Conn soprano other than the fully curved and the fully straight (and the stretch). As to Buescher's various tipped-bell and similar ones, I can only guess that either they were chasing the other semi-curved/saxello-form ones, or they were trying to eke out a bit more of the market. Someone who knows the chronology of development could probably provide useful insight.
If he sees it, I think Professor Cohen could answer and/or provide insight on these variant sopranos and their development; I recall more than one of his columns for Saxophone Journal dealt in considerable detail with them.
I have played considerably on straight sopranos (within the context of being mostlly a baritone specialist), a little bit on Yanagisawa fully curved ones, and not at all on any of the in between ones. A friend of mine who is a very fine soprano saxophonist loves his P Mauriat tipped bell soprano, and he swears it's not just a gimmick.