I installed a 1.5" butterfly valve a week ago and finally got to try it out this evening. WOW ! I have to agree that it is a big improvement over the ball valve for both the reasons you stated.
Yep. For me, it's a no-brainer. I just don't have the arm strength to quickly open the big ball without the barrel jumping all over. But there are a couple of issues with the butterfly ...
Yes, Stihl, the pressure rating drops from 600 to 175 psi. These rating are done under static conditions and, like anything else, they have safety factors. I'm absolutely no valve engineer, but the APTA application is a relatively easy application for a valve: 1) it is controlling air, not water, which weighs a lot less and 2) it only opens. It never has to stop a moving liquid column (think "water hammer" when you quickly close a faucet). So (just
me talking not TreeStuf) I'm OK with pushing it a little with a built-in safety.
I've tested my 1-inch butterfly to 240 psi. It behaves flawlessly and holds a perfect bubble test at that pressure. If the valve were to fail, it would not split the brass housing and explode. It would distort the butterfly pivot mechanism and the valve would begin to leak. At worst, there would be an unintentional discharge of the bag at some uncertain velocity. Regardless, proper muzzle management would say ALWAYS keep the barrel pointed in a safe direction.
Even with my testing, I never pressure my chamber above 215 psi That's one 16g cartridge for really high shots 150-170'. Most of the time, I use one 12g. Cheaper, easier on the bag and plenty of height., it gives me 165psi and 140' and the valve isn't even breathing hard.
Additionally, I've installed a poppet relief value at 215-225 psi. So, taken as a system, I'm operating inside a known tested region of safe performance. Again: me talking, not TS.
About the cost, there's a big saving when you drop to 1-inch. But there are issues here too ...
Now the style of shot goes from "rifle" to "bazooka" and/or "mortar". I particularly like the mortar so I can steady brace myself. Also, the ground resists the recoil so all the cartridge energy goes into moving the bag forward, not the APTA backward. Really good for the highest shots. But, if you only need a lower branch, you can shoot quickly and easily as a bazooka, you get a little recoil and it's almost like the APTA was automatically "dialing down" a little for a softer, lower shot.
And, surprisingly, the 1-inch valve is more efficient (higher) for the same volume and pressure on the chamber. The reduction coupling forms a little cup to cradle the bag and form a better seal to the initial air flow. Whodathunkit.
Of course, the best thing about the butterfly is the release torque. Down from 12.5# on the big ball, 3.5# on the small ball, and less the 1# on either butterfly. It's wonderful. But keep telling yourself it's now a TRIGGER not a HANDLE!!! Don't touch it until you're on target and ready to fire You don't pick up your Glock by the trigger, do you?
Sorry to be both long-winded and late with this. I wasn't ignoring the thread, I was gone for a week.
OF
I don't intend on pushing mine past 160 psi but like to fact check when the resource is around as I know a few operators using shop compressors to charge the APTA after hours for shits and giggles launching limes across the neighbourhood. 
