Mark is not the most personable guy, but I have some deep respect for some of his work. The Stealth barrel, while I do not like the lack of transparency in the metallurgy, has performed quite well, and I have a few, and we are starting a RECCE build with it. It is at least as good as Criterion. His rifles are dated in terms of design, but hold up nicely, especially the big bore.
His AR triggers are very good. I did a blindfold test between his MBT-2 and Geissele SSA and SSA-E, and just like the Coke v. Pepsi commercials of the 1970s, I was surprised at the results.
So, I would separate the man from the product. He can be very abrasive. He has a soup-nazi approach if you ask when your rifle will be completed, but there are days where my inner Mark LaRue come out.
So, take each product one by one. Rails are 10 year old technology. Mounts, sort of the same, but still do a good job if you need a quick disconnect. bipod mounts are superior, and the US Army chose his for the Mk22 with Harris bipod. Barrels are superior. Not an A+, but at $240 +/-, you get a darn good buttoned rifled 5.56mm barrel. Rifles are still contenders in 7.62mm, but he holds to the .260 Remington, when most have moved on to accept the 6.5 CM. He is a fan of the 6.5 Grendel, and I think everyone needs one, and if you are going to get one, you might as well get a LaRue. Generally, the upper and lower receivers are top shelf in terms of function and fit and finish. I don't personally like the integrated trigger guard, but once I get past that, they are pretty nice. As I mentioned, I think the Upper build kit is interesting. It is affordable, and there is a group think following to it, and design of the upper and rail connection is unique, but the aesthetics are missing.