I bought these basically for the aesthetic. I really like the sci-fi "mechanical" appearance of Milsig's rail covers. I thought they might be a little delicate but the actual product is robust, solid plastic! In fact, it may be a little too robust if anything; the covers fit really, REALLY tight on my picatinny rail. I actually had to file down both the rail and the undersides of the covers to avoid having to force them on permanently.
I definitely don't regret the purchase - installation just takes a bit of "persuading".