I agree with PH Racing, they're worthless.
The effectiveness of a comp is determined by its ability to trap and redirect the expanding gases. To do this, the exit holes for the bullet should be kept as narrow as possible. A bushing comp is limited by the large exit hole required to allow the barrel to pass through.
In summary...

Just my opinion.
Well I was of the same opinion as you,,,, I didnt really understand how they could work. And to be honest, I really just wanted the look of the compensator. My gun was already a pleasure to shoot, but the break just looked mean and I wanted one. So when it came time to order, I looked at tons of them, the wilson was the best looking by far and I got wolverine to order me one. The website said that you should use the guide rod kit, so I got one of those as well.
All in all, I was very pleased with the minor fitting it required, the finish was awesome and the overall look was amazing.... and then I fired it. I noticed an overall smoothing of how the gun cycled, and it just felt so nice when I pulled the trigger. The overall cycle of the recoil was soooo smooth. I dont know if it was the comp, the guide, or a combination of both, but damn, there is a very noticeable improvement on how it shot.... other guys might not feel any impovement, but I sure did, and I would recommend the wilson set up to anyone. Also, the ammo issue.... I had shot that ammo out of 3 different 1911's over the last year and always the same FTF issues every other mag or so.... today, 60+ rounds, same mags, same gun and not one FTF.
Any thoughts on whether or not the guide rod or overall set up effects the way ammo feeds, can a comp make a pistol more reliable...etc,etc,etc....????
FYI: I'm running this set up on a 5-6 year old Kimber Desert Warrior that has been tuned by Cape Custom. It has under 1000 rounds on this unit, but I have put 1000's of rounds of the comercial reloads through other guns, including Kimbers, Norcs, Glock's, etc.... all had FTF issues. Switch to factory ammo, no problems.... back to the reloads, issues again, and now after the comp and guide rod, nothing.... Has to be the set up!!!
Gord.