Most of the important points have been hit already. Kudos.
I have both a VLTOR MUR and a DPMS slabside like the one linked above. The DPMS is a huge, heavy and solid upper. As noted, its wall thickness will prevent use of some freefloat handguards. You can use it with a GI barrel nut setup, with a Midwest Industries Generation-2 one piece handguard (SS tube or T-series quadrail), or with many older style freefloats that use a barrel nut and jam nut arrangement (most YHM, oldest Daniel Defense, various others). As long as you plan ahead, it's not a big deal.
The other drawback to the DPMS is that it doesn't have M4 feedramp cuts, which most barrels being made today have. This isn't a big deal, but it's not ideal either. You can use it just fine with a barrel that has the feedramp cuts in its extension, you will simply have a funny intersection of the upper and extension, and theoretically not get the reliability benefit of the M4 cuts.
On the VLTOR MUR, for the most part I think it's awesome. It's forged, it's heavy duty, it has M4 feedramp cuts, and the ones made since 2010 or so have the profile adjusted at the barrel nut area so they will work with 99% of all handguards, including the ones with indexing tabs that overlap the receiver. The only small issue I've had with the MUR is finding that it won't fit easily with some of my lowers - ironically a Noveske lower in particular (ironic because Noveske has actually used the MUR on some of their rifles). The MUR is theoretically in wonderfully perfect dimensional spec, but I can't explain why it interferes with some lowers while most of my mil-style uppers do not. Still, this wouldn't keep me from buying one again.