All are equally good. I would reccomend any of the 3.
Trilogy Competition, SLIK Lite Cocking Block(bolt, pin, rod, block), KAPP delrin ball detent, grey Empire skull grips, Smart Parts on/off ASA, CP black rail, Macdev macroline kit, X-boarded Revvy, Nitroduck 47/3k steel, black Redz 47ci tank cover
Knob only moves 1/4th a turn
Can't be knocked into off position
It's an SP product
I got a Hybrid Grind on/off for 24 dollars with rail one day. It leaked after a little use, so the guy I bought it from traded me that for this so he could fix it, and maybe sell that Hybrid off(the color of this one matched my marker, unlike the Hybrid, so I got the long end of the stick). Comparatively, the Hybrid, Function, and this product are all easy to use, take as much effort to switch between on and off, and are all something to brag about having. I would equally reccomend any of those.
Initial use showed that it does it's job very well. There is no one hole in the ASA for the air to bleed into, there are four equally distributed around the pin. This isn't a selling point, but at least we know there will be air getting into the marker, and oil gets in without a problem. In the longer run, it's still holding up fine and is the one Smart Parts anything I have liked.
The niftiest feature of this ASA is that the knob only turns a quarter turn. You can't go past it, so turning air on and off is quick. Twisting it to the left turns the air off, and vice versa. It's no longer than a CP rail(the length of the trigger frame), so extended or shortened setups do not occur unless you mount it as so.
The fitting comes out of the front, and I have found this pleasing as well. It provides for the most low-profile setup your hose can have. Macroline would be perfect, since it can be cut to length.
The knob is on the side, and in turn doesn't move a pin inside the ASA that turns the air on and off. I haven't broken into it, and don't plan to, so all I can tell you is that it cuts the air off while the tank's valve is still opened.
I haven't found any weaknesses. It does what it should, didn't leak(even when used), the four holes around the pin makes sure your oil gets inside and gets friendly with metal parts, and is a real bargain. The only way it could get better was if it came with a rail mated or separate.