The purpose of the bevel on the guide rod flange is to provide clearance for the link in Commander-length and shorter pistols that have the correct Colt design lower lug geometry which places the flange close to the lug...AND...in such pistols which have a slight mislocation of the impact abutment.
Not necessary in 5-inch pistols and Commander-length pistols that have the frame's impact abutments correctly located. In this, it's a quick & dirty means to compensate for a little mislocation of the abutment without the need to remachine the abutment and rails.
It also aids in the removal of the guide rod from the slide during field-strip by creating a little clearance as the rod is tilted down and withdrawn from the bottom in pistols shorter than Commander length, and in pistols with a bushingless/reverse-plug recoil system.
In the above-described situations, it's a worthwhile modification.
In the pistols that use the bushingless/reverse-plug recoil system, the FLGR is nearly a necessity for quick field-stripping. These have holes drilled in them for bent paper clips that are used to capture the spring and allow removal of the system as a unit. In others...with standard recoil systems...it's an unnecessary affectation that serves no real purpose.
Shock buffs!
While they do soften slide to frame impact, there are some pistols that won't run satisfactorily with a shock buff in place. They reduce slide travel and runup, and eliminate the rebound effect on impact that helps to get the slide started on the way back to battery...providing more speed and momentum for feeding and chambering the cartridge. For the pistols that function well with a buff...they won't hurt anything, and do offer some protection. For the ones that don't, it's a decision for the individual to make based on how much frustration he or she is willing to put up with. I don't recommend a buff in any carry gun. Murphy's Law is in effect.
I use a buff in two of my high-mileage range beaters. The run fine, though the ejection is a little erratic because of the standard-length ejectors...but I can live with it. These pistols are gettin' long in the tooth, and have seen close to 165,000 rounds each on their clocks.
The buffs are a means to extend their service lives of the slides for a bit, and nothing more. The frame abutments are fine in these guns.
I have one pistol that is boringly reliable as long as there isn't a shock buff in it. Put in a buff, and it goes into spastic fits. Remove it...and reliability returns as though John Browning had waved a magic wand over it...and apparently only the pistol knows why.
