I think the Sp10 handguards work great. Having that flat bottom is way more useable than a standard slim hand guard for positional shooting especially in a heavy framed AR.
As for the proprietary mounting system, it’s just that, proprietary and has a purpose in the form of rigidity. Does it make a difference?? Well I can’t say 100pct for sure with ar10’s. I have seen a difference with bipod pressures, especially at distance with some of the longer rails using an ar15 that didn’t have a vltor upper.