I own or have owned all of them and I'll share my experiences. The Longoni extension is the most expensive and will damage butts with it's clamping action unless you are verrrrrrry careful every time you put it on and remove it. I know of 3 people who scratched a butt sleeve including me. NO THANK YOU!
The Hagar works, is inexpensive and is less likely to scratch a butt sleeve but I wouldn't use it on some of my higher end ebony butt sleeves that tend to show micro scratches easily.
The Tony Ryan is the easiest and fastest to put on and remove and is padded. I use mine every day and have never experienced a scratch regardless of which cue I'm using. I bought the strap on case for the Tony Ryan extension from Seyberts so it solved the old "how in the hell do I carry one of these things?" problem.
I do not claim to be an expert on gadgets but I can promise you this...since I have very little control over whitey and I'm a short guy, I have extensive experience using cue extensions---way too much experience.