my slx have been powerfull, modulatable, reliable, and other good stuff, for 2 years.
oh, yes, and cheap.
the olive+pin costs a quid, and i even like the split-pin pad retention system; there's no need to go mental and bend it over at a right angle, i've found that a simple little 20 degree tweak has been completely reliable, and re-usable, with the added confidence that it'll never seize in place with corrosion after a dirty weekend in the cellar… (i'm looking at you, hope).
as for 'quality' – i'd say it's top-notch, the levers are a bit different from the Xt levers, but not in any way that i could say is worse, or better…
if ever anything stops working, you can get a new calliper, ready assembled, with pads, for £25. and a new lever for about the same.
if you're not impressed, i would be delighted to take them off your hands.
i've got 5 sets of shimano brakes in the cellar (2 deore, 1 slx, 1 lx, 1 xt) and had zero problems for at least 2 years, the deores have been going for more than 4 years.
bleeding is about as tricky as any other brand, and the mineral oil is practically harmless, unlike dot fluid which will make your skin fall off.
the nukeproof 'enduro' pads are very good; long lasting and powerfull – about the same at shimano XTR 'metal', with the added bonus of being very quiet and a bit cheaper.
downsides: they're not 'sexy' – noone will ever point at your brakes approvingly, they're just brakes, and they work quite well.