Ever tried a Martin with the low A? They just made a handful of them, but they do not have the cylindrical extension, it's a whole new bell. (I've never even seen one let alone played one.)
Conn 11M and Buescher 400/Bundy/Selmer USA had the cylindrical extensions. Again, I've never played one of these but would like to some day when the work's all done.
Naw man, I’m a King S20 guy through and through. I used to be a dealer/repair tech and have played/owned/restored everything. I still have a Mark VI Bari (low Bb) that I love dearly, but there’s just something magical about the King’s quickness of attack and free-blowing edge on alto tenor and especially bari. Any bari that has a low A is going to play LESS well (less responsive, more sluggish) than the same instrument as a low Bb.
That being said, I can’t help but notice some parallels with the current existential crisis I’m in about locking in with a bass. My King Mortone is everything I’ve ever wanted in a bass, seems to play itself on the gig (effortless!), amplifies better than anything, feels great — but is 4 string.
All my 5 string basses feel like they’re in a suit that’s just a little bit too tight for them, especially around the collar - choked off, restricted. By comparison, the King feels like it’s in PJ pants and a T-shirt, ready to do cartwheels and handstands.
As much as I like to work up solo chord/melody arrangements on my 5 strings, I think at the end of the day that for 95% of functional bass playing the 4-string is superior, dang it.
The five strings have their place, just like the low A baris, but it’s at the sacrifice of that quality that makes them particularly resonant and thusly inspiring , methinks.