I've got one but in the years I've owned it, it's never got further than my reg tested
Ideally I plan to lash up a test rig to assess the effects of varying input pressure on reg output pressure before I stick it in a rifle. The only down side I can see is that, since the unit uses a coil spring as opposed to the more popular disc springs, it's longer than some other regs (Tench, HuMa) and hence displaces more cylinder volume / will give fewer shots per charge.
The coil spring gives more displacement per unit force than disc springs; which might be advantageous from a consistency perspective; but this is just conjecture.
As for the pressure gauge problem; I suspect that, if you're happy to float your barrel you can add an FTP900 filler and pressure gauge assy to the front of the rifle's cylinder (assuming you're talking about fitting the reg to an Air Arms 400/500 series, of course).