If you're going with a RDS soon then you might as well go with the MBUS. Cheap, light, good and strong. Also if it's folded down most of the time light weight is the most important feature. Still if you ever need it, it will work fine. All my ARs have one. The diamond aperture is nice but I'm so used to the round aperture I don't want to change now. If it works for you then sure, go for it.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek