On/Off ASA with Gauge - not as easy to release air
Carter Machine Custom Halfblock Sniper
+ Dye Angel LCD Single Trigger Frame with Universal T-Board
+ Dye Hyper 2 Inline Regulator
+ MQ2 Valve
+ WGP Dual Rod Modified Pump Kit
+ EGO Feedneck
+ XSV Profile ASA
+ CP 14" 2-Piece Barrel with Wire Detent Mod
+ 48/4500 Guerilla Air Tank with Ninja Reg
Quick Release Fitting
Quick Release of Air
Inability to directly turn on/off tank regulator.
I was lucky to pick one of these up last year from a retired old school tournament paintball player. Regular On/Off ASAs with bleed ports will function the similarly if a gauge is used, but this reg tester is able to release and shut off bleed air much faster and easier because it has a big knob. The only disadvantage is that unlike an On/Off ASA, you can't hook it up directly to an HPA tank reg to check output pressure. Instead, you need to hook up the tank to an ASA with either a steel braid and quick disconnect, or with macroline to a gas thru grip.
The burst disc is a nice safety feature so that you will not blow the gauge with a supercharging regulator. The gauge is big and easy to read compared to a mini gauge.
It's too bad these aren't made anymore, since most modern markers don't need them for fine tuning. They are more useful for tuning autocockers and snipers, or for airsmiths in diagnosing problems.
If you like to tinker, this is worth picking up if you can find one. It makes quick work of checking air pressure out of tanks and regulators.