Cheap ... for a reason - XTS Mil-Spec 6-Position Buffer Tube

The other 1-star review of this buffer tube hit the nail on the head. The "head" of the buffer tube is not milled and drilled correctly for the buffer retention pin. Either you screw the tube in enough that the buffer retention pin is properly captured -- but then the top of the buffer tube fouls the upper receiver; or you don't screw it in enough for clearance but then you can't use a buffer retention spring.

Or, you get your dremel or flat file and you file down the top of the buffer tube so it doesn't foul your upper receiver. It's not a whole lot of work (5 min max) and is something that's fine to do with your plinking toy; but maybe not something you want to do on your SHTF weapon. I figured it was worth the trade off, but it doesn't take away that this is not mil-spec because of the lack of proper milling.