Does anyone have any experience with these?  I am thinking about buying one of their new kits for the G21.  

The price ($249.00) seems reasonable...

I bought one for my Glock 17.  A lot of fun and it functioned flawlessly.  I think I paid $250 for mine as well.

They are great. Fit, finish and function are great. You can plink all day for $10. It's a great tool to introduce newbies.

You can get a ruger .22lr for the cost of that conversion kit, and have 2 guns instead of two.  A .22 pistol is much more accurate than a conversion kit, too.

Some people think that shooting your glock with the AA conversion is a good way to practice, cheap.  But with the difference in recoil, weight, and sights you really only have the grip angle the same.  Granted, it is better training on a glock than using a .22 pistol, but not enough to adequately prepare for any competetion or real world situation.

Good points,I just haven't analyzed it that much.  I do like the idea of multi-caliber handguns.  With a conversion kit I can go hiking with a holstered Glock 21 in either .45 ACP or .22LR and have the slide assembly and mag for the other caliber nearby.  This would give me two calibers while saving the weight and space of two handguns.  That and always wanting a .22LR Glock are my main reasons for wanting one.

The people over at Glocktalk love thier Advantage Arm conversions. On thing you can do with the Advantage Arm kit that you cant do with others is change the sights. You use either the Glock cup and ball set, or put on some 3 dots or ashleys on.

Another vote for the advantage arms kit.

DallmannTodd: Im sorry but I have to disagree with you about it not being a good training tool. There is alot more than just a grip that is the same. Trigger pull, grip fit, familiarity with the sites, and the firearm. Its a perfect way to train. Much better than going with another different handgun thast unfamiliar to you
But I WOULD NOT say its the only way to train. Useing full loads are the only way to get that real feel to it.