Back in the 2000s, one of the only options was the Rock River 2-stage, unless you wanted to shell-out for KAC or Jard.
The RRA 2-stage would hang-up on DPMS LR-308s, arresting the BCG in the rear position until you let go, so a half semi-auto. The sear engagement in them also wore out quickly.
Also, on the Geissele adjustable NM High-Speed triggers, you really need to dial-in your sear engagement to prevent them from doubling. This is true for any adjustable trigger that allows you to set the take-up to be right near the bleeding edge of release. If you ride that edge, you will likely have doubles. Not a failure per se, but an incorrectly-adjusted/set-up trigger.
Some of the hammers made with lightening cuts or skeletonizing can break in extreme cold or even low round counts.
Imitation hammer and trigger pins can crack, especially the hammer pin.
80% lowers that haven’t been anodized will slowly egg out the hammer pin holes, which is why anodizing is part of the design/TDP.
The companies that use certain tool steels and have a culture of holding to very strict tolerances and production QC are the ones I lean on.