Consider maintenance.
You currently own ScubaPro.
Both the Air2 and the SS1 are high-quality kit that should function as designed. The amount of time you'll spend on them over the next ten years will be measured in minutes. It's largely irrelevant which one you get.
But having to take one set of regs to one place for their annual overhaul, and then pulling your whatever off your BC to take it to a different place for annual maintenance would suck.
And if you're going to go with either, thats part of the price - maintaining your 'inflator' after each dive exactly as you would a regulator - including annual servicing...
Unless your LDS carries and services both, I'd suggest you consider going with either all SP or all Atomic.
FWIW. YMMV.
PS. to Scuba Two - the range of motion available with a secondary/inflator depends on the length of the corregated hose - not the device on the end of the hose. If its too short, get a longer corregated hose. Which will cause different problems, but either way, inconvenient inability to move your head while using the thing as a regulator isn't the fault of the secondary/inflator.....