simply put, if you are having gas issues, want to fine tune your cyclic rate, or want to install a JP LMOS, go get one of these things.
Four major reasons:
1) it fits under rails unlike so many other adjustable blocks (ahem, PRI),
2) it adjusts easily from the front which is absolutely necessary for tuning the rifle and somehow nobody else has figured this out
3) it has a press-to-turn detent which prevents the gas screw from backing out unintentionally (no need to worry about locktite)
4) if you are replacing a set-screw gas block (one that is secured with screws going 'up' into divots in the bottom of the barrel) then the spikes' block is a drop-in replacement. Fits perfectly where my low-profile PRI block used to be.
I installed it on a Bison 6.8 that was having gas system issues, and with a couple turns of the front facing adjustable gas screw, my AR was cycling perfectly. The adjustment is super easy - no need to drill out or remove your rail system to get access. Just make sure your gun is unloaded!
One tip: bring along something to press in the detent...a 1/4 inch allen wrench has worked well for me so far. Doesn't need to be anything specific, could even be a chopstick, but if you have rails that extend over the gas block, you want something long and wide enough to press the detent down while you turn the adjustment screw.
Another tip - if you have never adjusted a gas block before, turn the gas screw all the way in, load up a single round in a good mag, aim in a safe direction and fire the rifle. Check to see whether your bolt is properly locked back. Properly locked back means that the bolt catch is holding back the actual bolt face, not just the bolt carrier. Keep opening up the gas block screw 1/4 to 1/2 a turn until your bolt properly locks back, then go another 1/4 to 1/2 just to be sure (and to give your gun enough gas so it can accomodate variable ammo loads)