I have two .40 Glocks. I feel the KT is noticeably more compact, though if I KNEW I was headed toward a conflict, I would prefer to be carrying my Glocks (longer barrels, more ammo, shorter trigger pull- but larger). It is just easier to carry a Kel-Tec concealed.
As for reliability, I have had as many problems with malfunctions in my Glocks as I have in my KT's. I have had some failures to chamber with my P-32, but this had been using FN .32 hardball that would not function more than 50% of the time in an unmodified Guardian. (Spartacus had to polish his Guardian's feed ramp for it to reliably feed even Silvertips, btw.)
I don't recall any malfunctions with my P-11...