My first single hose regulator set was a 109 and a Mk5, bought in 1972. I still have both, and on occasion dive with them. I upgraded the 109 to balanced adjustable many years ago, very easy to do. The old Mk5 has only two LP ports on a swivel, and one HP port. I use the combo very seldom, and only for shallow solo dives since there is no port for another second when the BC is attached. The HP port is too small for current SPGs, but there is a fitting that converts the HP port to modern specs. I converted the Mk5 to DIN with a Scubapro kit made for that regulator. Both units have survived for a half-century quite nicely, and though I now dive mostly with a Mk10 and a G250 Graphite or D350, I still enjoy taking my old friends into the water once or twice a year. As far as performance goes, I notice very little difference, and I use steel HP tanks (3440) with no problem. Needless to say, I do all my own work on the regs. Except when on vacation, I dive only in summer ( I'm shockingly old) when local waters are warm enough for my 2.5mm suit, so on many a winters evening I take everything apart, replace parts that still look fine, and use a degree of care and cleanliness that might be considered excessive by NASA.