I haven't rebarreled any Glocks, but have done so with Colts and FN/Brownings. Haven't used KKMs myself, but a gunsmith I respect told me he has used KKM barrels. As he has demonstrated his knowledge and skill in doing some excellent work for me, this is enough for me to believe KKMs are likely a quality product.
Within the past year, I have used two Storm Lake Barrels. Both excellent in every way IMHO. I have also used several Bar-Sto, Kart, Schumann,etc. I wasn't initially sure about Storm Lake, but have found nothing to criticise about them. I would not hesitate to use Storm Lake again.
BTW, from past experience, I would prefer that pre-fit or semi drop-in barrels do not actually drop right in. Most barrels internally are fine, it is the fit of the barrel-to-slide-to-frame that makes the difference. Irv Stone III of Bar-Sto indicates, on a video, that his semi drop-in barrels are are equivalent to his gunsmith fit barrels, if they do require a little fitting. My experience with both semi drop-in and gunsmith fit barrels over the last 30 years or so seems to confirm what Mr. Stone says...ymmv