Like I mentioned I did try them once, it did tighten up the rattle in the rifle I tried it in. Didn't change accuracy one bit on the target.
My final opinion is pretty much if you like the results, great use it. But it does not add to anything, except fitment of the upper and lower in my experience. To some it is worthwhile, as the rattle does bother them. That does not mean that it couldn't just in my case it didn't. But it did "sound" and "feel" smoother in operation, which honestly is not a measurement in reality in my simple opinion.
I don't even consider it any more if the AR I have at my disposal rattles, no problem, provided it meets my accuracy needs. If it doesn't perform to my expectations I look every where else except the upper and lower mating. I'm not discouraging the thought, or practice. Just my limited (meaning I'm not working on YOUR rifle) experience is it's just not the cause. Will I swap to get the best fit possible with a upper and lower in the start? Yes, but it's not a requirement.
Does it discount the idea? No, if one desires a tight fit whom am I to say they are wrong or foolish to seek such. If they feel that it will improve their rifle in some way.
Personally I'm not on either side of the fence, nor am I on the fence. I simply don't focus / consider on it. Just rather what it shoots like as it sits. If it does not perform the barrel is the first suspect in my mind, after I check the barrel nut tightness / alignment.
Could it egg out a take down pin hole? yes it could, just as much as any misalignment would as a example with a tolerancing stack up.
Should it? No, the material "should" give enough support or upward pressure to have a proper alignment yet provide support by it's design concept.
I've seen others offer in the past a set screw from the bottom of the lower to do the same effect in the past. But funny you don't see that anymore being offered. I've seen like many of ya'll other companies offer "shimming kits", steel sleeves to insert into the upper lugs, etc etc... all have fell by the wayside over the years.
Yet the accu-wedge remains as the least evasive attempt for this idea. So honestly would I condemn or promote the concept. Neither is the answer.
Does it make a "difference" ? Depends on what is the difference sought. Some would say yes, some no.
Like hm1996 pointed out on confidence I've seen gunsmith's use a bore scope to their advantage with customers let them look down the barrel, talk about how bad the barrel is.
Now the customer can't hit the broad side of a barn, when before they could produce decent accuracy. Naturally a new barrel was installed, the customer now happy.
I "had" a Rem 700 in 7mm Mag that he tried the same trick on me, which I refused to look at the scope. Instead I just shot the rifle to evaluate. 5 shots cloverleafed on target at his range he sat there in disbelief ... my son now uses that same rifle with it's "pitted" looks like "5 miles of bad Georgia backroads" factory barrel (IIRC the barrel date code was 1963? maybe 1965 not sure but I do recall it was earlier than 1968). To harvest game every year, my only advice was to him never look at the barrel with a borescope, it will scare the accuracy right out of the barrel. (same ole girl, different dress)