Few thoughts on “slick” rails, and yes you should upgrade from the quad pic-rail system. Weight, modularity and handling are really improved.
I have a Centurion Arms CMR rail, this is their proprietary ultra low-profile handguard and it mounts very easily and securely with anti-rotation tabs as well. The machine work is phenomenal and they have a very unique look to them. Definitely the slimmest handguard I’ve owned but still built like a tank. They come in Keymod and MLOK as well for those that don’t want to use the CMR system (personally I like it, but others may not want to get additional rail accessories). Monty was a former team guy and his products are purpose-built towards the “operator” community which spills over to be pretty useful to us general peasants as well.
I also have a Geissele MK16 which is their pic-top with MLOK on the 7 other sides, really endless mounting potential for whatever you want to throw on it. They have other variations depending on how you want the 45 degree faces to be, all very well built and the finish is among the best I’ve seen. I’d say the MK16 is the lightest slick rail I’ve owned.
I have not personally owned but I’ve handled the BCM MCMR and seen the KAC URX4. They both look very well engineered and in a similar tier with Centurion and Geissele. I’m sure the Daniel MLOK is great too I just havn’t laid eyes on one. Can’t go wrong with any of these, buy once cry once.