Put me in the very strongly "FLGRs are generally a detrimental modification to a good 1911" opinion category.
As a 1911 enthusiast since 1974 who has shot, tinkered with, gunsmithed and competed with the 1911 platform extensively since then I have cause for my opinions - and my opinion is to change any non-racegun 1911 Recoil System IMMEDIATELY back to John Moses Browning's original design, when physically possible. I have worked in an American Pistolsmith Guild Gunsmithy, where we customized hundreds of 1911s for customers, and we built "magazine feature guns" you have seen if you read American Handgunner and a couple of other famous gun rags. For most customers it was "stylish", but a waste of money and an inconvience you were paying to add!
I have personally used the FLGR in IPSC competition and on the shorter 1911 carry guns, and after many years of observation come to the conclusion that it is undesirable except in certain, very limited circumstances that don't apply to most, normal use guns and owners.
Testing by numerous commentators have shown zero to negligable benefits of installing a FLGR. There are no accuracy or reliability benefits that were not reflective of another problem in the subject weapon. I have been doing this a long time, and I have never seen or heard of a legitimate case of the claimed problem of spring breakage mentioned here, and I would assume any such weapon must have some tolerance/machining/material defect to produce this result. Well over 5 million weapons of this basic design type are in use around the world - if this was a real problem it would have become known as such sometime in the last 99 years of actual use - and would have been corrected sometime in the 75 years the 1911 was US military issue.
What are the negatives of the FLGR? Difficulty of disassembly without a tool, usually requiring a bushing wrench or at least a paper clip for takedown. In the woods, or after getting the weapon wet in salt water, or dusty/sandy I want to clean it NOW, not a week from now when I get home to my toolbox. And no, I don't take my gun box, a bushing wrench or a paperclip to the woods or on the water. All of my bushings are deliberately fitted to allow removal without a bushing wrench, even if "snug". (Allen headed grip screws fit this same category of pretty but really hard to find a wrench in the field when you need one.) My guns are tools, not toys, and functional and servicable in all situations matters to me. I prefer a gun that requires no tools to fully disassemble and reassemble in the field - like the original 1911.
In a Law Enforcement or self defense context, the full length guide rod prevents one handed operation of the 1911. If you have a hand injured or occupied (say with a flashlight) and you have a malfuntion with a standard, full sized 1911, you can push the bottom edge of the slide against any hard surface (or your boot) and cycle the action with the shooting hand only. The guide rod prevents this. If you have a square rear sight - not a Novak style - you can substitute this as your charging handle, although it is hard on some sights. If you have Novaks and a guide rod, it is pretty near impossible to clear the weapon effectively without two hands. (If you attend realistic training with photographic or anatomical targets of "bad guys" with weapons in hand, at the end of the day you will see that there are a lot of rounds clustered in and around the hands and weapons - the subconcious mind aims for the threat, even if the concious mind thinks it is going for center mass. The likelyhood of injury to the hand in a gunfight is much higher than generally understood.)
Where could I see a use for the FLGR? In a competition gun, where the extra weight (particularly if made of a heavy (expensive) metal like tungsten would put weight on the muzzle and help with recoil and muzzle rise. I would not care to carry that extra weight on my belt everyday, however, and I prefer to train with the same tools I might have to fight with.
In the shorter 1911 lengths, particularly the 3" class of weapon, the guide rod is necessary because of the bull barrel design - it simply can't be helped if you want the weapon to work in the small configuration. Bull barrelled 5" competition guns also require the reverse plug design, but again, these are generally race guns - not for "real use", and again, too heavy for carry.
The standard 1911 JMB design supports all but about 3/8" of the installed length of the spring at all times anyway, between the length of the recoil spring plug and the length of the recoil spring guide. What are FLGRs for? Mostly, as a fad, "to sell" to those who don't know any better. Except in the few and rare noted exceptions above - run your 1911 the way God and John Moses Browning intended! Just my opinion, but an experienced and reasoned opinion. CC