I think they make decent stuff. Obviously their bottom end is a bottom end just like Shimano and SRAM do as well. I think they frequently get denigrated by people in shops because of heavy bias and old crap that gets passed down from grumpy old mechanics or inexperienced mechanics who probably also heard the old gobbledygook.

I haven't seen any issues with Advent beyond a hard worn derailleur that was crashed and used a lot with some heavy mountain biking that needed replacement after a bunch of years (and was still working just not getting into all the gears anymore) but beyond that everything else has been great quality and they are one of the few companies still doing bar end and proper thumb shifters. They also make shifters for 10 speed road stuff pre-4700 (which is a 10 speed group that is technically 11 speed cable pull) which has been a huge boon when we get 4600 stuff in that is worn out or broken.

They also make a lovely super short derailleur groupset which is great for kids bikes or folding or mini velos something Shimano or Sram do not really have. Pretty much so long as you go with 10 speed and above you will have good stuff generally but I will say pre-CUES I would have said regular Advent or Acolyte is slightly better than the Shimano low end crap but now CUES is making Shimano look a lot better.

All in all not the best of the best but a good lower cost alternative and some unique bits that the big brands don't want to tackle. I would generally rather spec higher end Shimano but if I was building a budget mountain bike or gravel bike I don't think I would hesitate to use AdventX or Sword.