As with any holster, Kydex will eventually wear on the finish of your gun, especially if it (the gun) is blue. However, Kydex is not especially hard on the gun as it is a thermoplastic and considerably softer than the steel of your gun. Also, Kydex holsters do not make contact on the majority of your firearms surface, so you will have wear points instead wearing the entire surface.
The only real concern is to keep dirt, small rocks, etc., free from your holster; such debris can get trapped between the Kydex and your gun and WILL scratch your gun's finish.
As far as BladeTech quality, I have seen some that work and fit perfectly and some that belong in a trash bin. Personally, I believe tensioning pins belong on a combat holster like adjustable sights on a combat pistol (they don't.)
Sidearmor makes some pretty cool stuff for Glocks. Naturally, my personal favorite for strong side hip is the GunGlove Taylor Thunderbolt.
Tim
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