I use the same length inflator hose with my Seatec as I do with my wings, a 22 inch I think it is.
The Seatec Sunfish has a dump valve and most certainly is a buoyancy compensator in all senses.
Mine, a military Sunfish bought new from Kenlees with a USD patch sewn over the Seatec.
There is a blue and yellow Seatec brand new for $220 at the shop across from the Scuba Club.
It is true most people remove the CO2 cartridge and install a plug but you could certainly leave the cartridge in place. On all of my BCs, wings or otherwise, I remove the dongles and tie a double knot in the end of the string and burn it tight. Works much better and does not get hump up constantly or in the case of the CO2 cartridge would not discharge it. Pulling the cartridge at depth is a non event, at 10 feet or so it would inflate nearly fully but at depth, hardly at all.
James