But the main one is that you're a bike snob, and you can't help trying to upsell someone who came here for advice fixing/modifying his bike. Bicycle shaped objects are a problem for mechanics, but this is not one of those it's an entry level hardtail. So it's not going to win any races, but it's perfectly adequate for fitness and fun riding on or off road. Yes cheap Shimano hydraulic calipers work fine, and cost less than alternatives, but if you lose confidence in a bike it ceases to be fun, and that seems to be what happened here - give the guy some alternatives, and maybe some prices, and let him decide, don't just tell him he's doing it all wrong.