Supposedly the net positive is that, as the gun recoils, the recoil spring doesn't bend inside its channel (the dust cover), making the gun smoother in recoil and control. I haven't seen anything or anyone that says such a thing is truly important to making the gun reliable.
Net negative: the 1911 is a gun you can take totally apart with your hands and empty 45 case. You add the FLGR and you need a tool.
The above assumes that you're not setting up your 1911 with any barrel different than a classic 1911 barrel, if you're using a bull barrel then it's a different game entirely.
Basically, for most users, you don't gain enough to make it worth the trouble.