I have 2 Delton lowers about 10 years old with thousands of rounds on both of them. One has a nice finish the other had a really dull rough finish so I painted it. Haven't had any problems with either they're mil-spec.
I had one factory built Delton I sold it a few years ago. It had a 1-9 twist barrel 55gr was most accurate "around 2 MOA", no m4 feed ramps, trigger was really heavy/gritty, and it had a commercial buffer tube.
Wasn't a bad rifle though especially for the $400 I paid. Never had a major problem with it. It didn't like steel cased ammo.
Definitely not mid quality. Had a basic upper years ago and the chamber was so rough it would barely feed at all. Took it back to the shop and the owner said I wasnt the only customer with those complaints.
My understanding is that they used to be firmly "meh" quality, but in the last few years has improved to "ok" to "decent" quality. A friend of mine has a 16" carbine upper from 2017 that shoots about 3.5 MOA with bulk ammo which is honestly not terrible. Not sure what he could get with match ammo but we literally never shoot it so it doesn't really matter to us. I don't think he's had any failures with it in a couple thousand rounds.
Have built a couple of their kits over the years. They were reliable and accurate. Upgraded to Bravo Company bolts and put many rounds through them over the years. I'd say they are on par with a PSA or S&W rifle.
Had a 60 some year old wanna be sheep dog with a Delton come in Lets just say I wasn't impressed with either. He couldn't get it to hit paper so he wanted me to try. The rounds were keyholing
Upon questioning he just bought a Chinese flash hider off Wish he just put on. Removed the flash hider and it quit keyholing but was barely sub minute of target at 50 yards (and I pulled some multiple brand decent factory rounds to try because I was like WTF so it was in fact the gun)
I'd stay away from them. (both that dandy and the Delton)
I've had mixed luck with Delton. 2 of my uppers are superb, some of the others, not so much. A bit rough in fit and finish but the 2 I kept shoot very well.