As has been said already it's a matter of what fits your needs. Sometimes they break, as can any system on an RV. I would not base the decision on complaints about failures as a gauge of reliability. After all people don't post "Hey I went camping last weekend and my slideouts worked perfectly!".
Overall I would say that slideouts are probably less prone to failure than some other systems. On my trailer I've replaced the water pump, the tongue jack & the converter in 7 years, but the slideout works just fine.