What makes mil-spec better (in a 22lr)? It just means that mil-spec parts fit it and for those particular 22lr uppers, it just means they're gonna fit a standard mil-spec lower.
That is what the military wanted when they came up with the TDP (Technical Data Package); parts that would perform reliably under combat conditions and fit multiple platforms, not what was the best parts you could fit on an AR. And those materials, measurements and quality control testing are all part of the TDP which give the blueprint to what goes onto/into a "mil-spec" firearm. That makes it so all sorts of different platforms have interchangeable parts which makes life much easier while in battle and when you're trying to make sure not to run outta certain parts and having to stock too many different kinds of parts.
To the common shooter, (well to me anyhow) all it means is that you know mil-spec parts should fit, not that it's gonna be more accurate. I sure know that I'm not blowing through 200 rounds in just a few seconds so some of the mil-spec testing doesn't even really apply to non-full-auto firearms...Although I'd love to have a full auto.
Honestly, the term "mil-spec" is so over-used and misunderstood to the point it garners the same disdain from me as the term "epic fail".
As for the Spikes, the price of just their uppers go for $560. You'd still need all the other goodies to buy just to shoot it...plus they also call their barrel "match quality", not match grade. And I've just talked to too many people who didn't like their conversion kits to ever consider putting one on my Stag AR which is why we went with the M&P.
The 15-22pc model was built from the ground up as a dedicated high-end 22lr platform that has two stage trigger, nice grip, match grade barrel and chamber along with other goodies. I'd take a match grade barrel and chamber over being able to stick a 22lr upper onto my mil-spec lower any day.
I'm not doggin Spikes, they make great AR's. I'm just sayin, in this case, for a high-end 22lr, I don't think a mil-spec upper stuck in an AR lower can compete with two stage triggers, match grade barrels and chambers and nice grips along with being manufactured as a dedicated platform...but that's just me and my .02.
And it's only the receiver and charge handle that are mil-spec on the spike's, it's actually "mil-spec featured", not mil-spec as to my understanding of the term mil-spec.