I have a Magpul and Smith wrench . No idea why the Magpul wrench is so special because it doesn't do anything appreciably better. Having said that, the Smith is not cheap either !
I also don't know why lots of people want a "do it all" wrench . Couldn't care less that they have 5/8" and 3/4" openings . Who doesn't have open end wrenches that size !
I have taken off a few ungodly tight muzzle devices and I would much rather use a quality wrench like a Snap on Flank Drive ( doesn't put pressure on corner )
My most used by far is the PRI wrench . Reason for that is it can take std barrel nut but also most of the proprietary barrel nuts such as PRI , YHM, KAC FF ( exceptions like the DD and KAC URXII )
http://w .brownells.com/gunsmith-tools-supplies/rifle-tools/wrenches/ar-15-m16-barrel-nut-wrench-prod27412.aspx
There is no way in hell you can have the PRI wrench slip off
Much easier to handle with torque wrench
Only downside is you would have to remove the A2 front sight to slip wrench over . Thats the only time I reach for my Smith / Magpul . Even without them, taking off A2 front sight is easy with the right tools ( cradle and concave punch) )
For castle nuts, just buy a dedicated buffer tube wrench
Lost available from the cheapy RRA ( I used one for years and it worked fine ) to the Brownells at over $60
IMO , take the extra $$ you save buying the PRI wrench and RRA and put it towards a good vise block ( I use the PRI ) and a Geissle reaction rod or the Brownells version of that