Woo just received 6 of the 84hp rails along with 3 pairs of 3U and 1U end plates, right off the bat, they are really nicely made, one minor suggestion is to add countersinking to inner face of the end plates to allow for more fixing options.
I get the screws provided are intended to fit nice and snug, but if I want to build a case fully out of metal then machine screws the same as those provided for the rail fixings would be my choice.