My experience with the 6.5 G ultimate upper has not been great. While the machining and cerakoting were excellent and the free float design is solid, the barrel to receiver fit was sloppy and loose. The barrel wouldn't shoot sub-MOA with factory ammo and my reloading efforts were less than ideal (maybe .7 MOA at best). I even put in a new carrier, an SSA-E trigger and a JP SCS, which did not help much. To Larue's credit, they were very good about sending me a label to send it back and they returned it to me with a new barrel. I haven't had a chance to shoot it yet, but I'm hoping the target then sent back which had three shots holding .6" is a good sign. However, I am tempted to just sell the barrel before shooting since it is a little heavy for field use and just get an 18" JP barrel.
Larue used to be one of the only options for match-grade ARs, but has been behind the times for a while now and is playing catch up now that the AR market has softened while there being newer and innovative options. Overall, I don't think it is worth buying the kit unless you like all of Larue's parts and are looking for field grade rifle in terms of accuracy. For that, I'd take a BCM all day, every day.
I ended up selling most of what the kit came with except the upper, barrel and BCG. Personally, I don't care for their stock and grip. I also don't like the MBT trigger I prefer a Geissele SSA-E which can be had for only a little more than the MBT when on sale. The buffer is just standard carbine weight and the carrier is an unknown contract manufacturer. The buffer tube was not any nicer than a Milspec BCM or VLTOR. Larue's billet lowers are okay, but as Jake noted above lack modern features such as a short throw safety option and ambi controls.
I also think it is a crap shoot on getting a really good barrel (at least for Grendel). If you look at the threads in the Larue forum on ARF dot com there are few guys that have good results from factory 6.5G ammo. However, the vast majority are three shot groups just under an inch. Most won't post five shot groups, and those that do aren't that impressive. Given my prior experience with Larue and JP, my standards are a lot higher than what Jake is right to call fanboys. If you really like their upper design, it would probably be better to just buy the stripped upper/rail combo and buy a better barrel and BCG.
I put a 6.5 CM together with a JP barrel, and so have several of my friends. We all see .5 MOA with them, so I'd go JP over the Larue if you are willing to spend a little more.