I haven't heard any dependability issues from any of them to be honest. The trade offs really come down to preference issues. If you are looking for something to learn on for dealing with newer air barrel designs, the 109/156 will be the way to go. For bullet proof simplicity a 108 (or USD Conshelf) is the way to go. A balanced second stage will go longer without needing to be retuned, and won't react much to changes in intermediate pressure (read that as unbalanced piston first stages). An unbalanced second stage will need retuned more often, and will breathe stiffer as IP drops (read that as dropping tank pressure with unbalanced 1st stage). Main benefit of a 109 vs. a 108 is the ability to crank down the adjuster to reduce chance of freeflow when using the 109 as an octo. Seats for a balanced reg cost more, but last longer. So it all comes down to preference really.Thanks for sharing that info! From what I understand the 109s are a bit more dependable. Is that true.
Just my opinion... but I find myself leaning into the Conshelf/108 designs more. Dirt simple, reliable, and breathe great if tuned properly.
Respectfully,
james