We have three large cable slides on our 2012 Open Range 345RLS and love them. We've had our trailer for over two years and traveled 19,000 miles with lots of moving the slides in and out with no problems -- zero issues!
Yes, we do check them (it's called preventative maintenance and is recommended for everything on an RV) to make sure the correct tension is on the cables and adjust if needed but that's very easy and done inside the trailer. We've never had a water leak and we've been in some very heavy rains. (10 inches in 24 hours this spring!)
There are going to be people on here tell you they're a bad idea, they don't work, they break, they don't like them, etc. but those will be the folks who don't have them and therefore don't know what they're talking about. ;) We wouldn't want another kind of slide now that we've had the cable slides. Ours are the Bal Accu-slide.
BAL AccuslidesEdited to add: If as the previous poster stated the cables stretched -- they are easily and cheaply replaced. You can get a set of replacement cables for $25. from Amazon and the installation is a quick and easy job. Certainly easier and cheaper than replacing electric motors or hydraulic systems. We have friends who had a huge oil leak under their bed from their hydraulic slide out. Yuk!
Peg