I did watch the Military Arms Channel video as well as the Small Arms Solutions video. They were both very informative, but that’s the extent of my knowledge. I’d like to add one to my collection simply because it’s a unique design. I’m open to getting a 5.56x45, 6.5 Grendel or 7.62x39. I’m more inclined to get an SBR, but would like to be sure they run as reliably as a full length rifle. Most importantly, I’d like to know what to avoid when buying one. I see on their website that there are different handguard lengths and hidden gas blocks. What are the advantages/disadvantages of a hidden versus exposed gas block? Other than that, I don’t know the questions to ask, but am eager to learn.
If reliability with any mag is your goal, 5.56 is the best bet.
The SBRs may take a little more work to get running 100% than the 16" bbl or longer....that's just been my unlucky experience owning 10 XCRs. You will probably get a good one and won't have to worry about it. If you do have a problem, RA will fix it....though that may take a while. If you decide to go it alone and void your warranty....this is the stupidest simple platform you can buy and with relatively few tools, you can fix most problems yourself. The forum here is pretty good with diagnosis....
I personally wouldn't shy away from older versions....but if you want all the upgraded/newest configuration items.....you're better off buying new from someone like Nate or Kermit than to buy a used one "cheap" and then upgrade it (I've done it both ways....from a cost standpoint, you're better off buying new).
IMO, the Type 3 gas system is the best....though the Type 1 works just fine even with SBRs...it just doesn't have as much adjustability and the gas dial design, while easier to take apart, is more susceptible to getting launched down range if you make the mistake of not having it properly positioned (I've never had this happen, but there have been 1 or 2 people that have come to this site that have). Stay away from Type 0 gas that requires a tool to adjust.
The "enhanced trigger" is another must have, to me. It's much better than the original.
Handguard length is completely subjective as is gas block placement. That said, on a DI AR, the longer gas systems typically run smoother....but you have to balance that with gas port position and dwell time when talking about running SBRs. Keep in mind though...this is a long stroke GP gun....and that's not an apples to apples comparison. Personally, I try to go with the longer gas systems when possible on the SBRs, but I've never run a micro length XCR either, so I can't compare. I don't notice a HUGE difference with a mini vs. stnd. length gas system other than the fact that the shorter bbls that required the mini length gas do have more recoil...but again, it's not a massive difference even in 7.62x39 (or .308 in my 12" bbl -M).
Hidden vs. Exposed gas blocks...again, personal preference. If you have a Type 1 or 2 Gas block...you can't hide either of them. Obviously exposed blocks are much easier to adjust and do any maintenance on...but I do really like certain bbl lengths with the buried Type 3 block in terms of the look (16" bbl competition length HG w/ stnd length gas and 9.5" bbl stnd length HG w/ mini length gas).....but a 9.5" 5.56 is ballistically losing a lot over an exposed 11" bbl....so you may want to go with practicality over looks. Besides, it's largely personal preference.
HTH,
Sean