I had two of them (KKM) and I find they are the best of the "drop in" barrels I have used. No fitting is required with these, but they do have tighter tolerances than the Glock factory barrel. I much prefer them to the Lone Wolf barrels which sometimes have too tight chambers and the hideous wolf logo. In my KKM barrels, I had about 5% of my reloads which were too big to chamber in the slightly tighter KKM chamber. My Lone Wolf barrel would not chamber 30% of the same reloads. Stock Glock barrel would eat 100% due to its generous chamber size.
I found mine to be slightly more accurate than the stock Glock barrel. However, unless you want to shoot lead, I would stick with the stock barrel.