IMO, the biggest downside to a Schwintek (and "cable" type) slide is the use of plastic rollers underneath the slide to support the entire weight of the slide. The Schwintek mechanisms move the slide in and out of the trailer, but they do nothing to support the actual weight of the slide. These rollers (underneath the slide) are usually mounted on the very edge of the wooden floor---within inches of the outside wall of the trailer. Support for the wood floor underneath these rollers varies dramatically from trailer to trailer. I've seen anywhere from zero, to 2 to 3 metal outrigger supports underneath the wooden floor supporting a Schwintek slide. On smaller, lighter slides the lack of support may not be a big issue. However, on medium to larger slides this lack of support may rear its ugly head years later when the wooden floor starts to sag from the excess weight---causing all kinds of alignment problems with the Schwintek mechanism.
When we were looking at trailers last year we ruled out purchasing any trailer that didn't use rack and pinion slide mechanisms on any medium to large slide. With a rack and pinion slide mechanism, the entire weight of the slide is supported via two large steel beams that are inserted directly into the side of a trailer's steel frame---no wood involved.
IMO, a Schwintek mechanism is pushing its operational limits if the slide extends out more than 24", or if it has to support any human occupants or heavier appliances (especially fridges).
Lastly, rack and pinion slides typically have fore and aft, up and down, and in/out adjustment points to compensate for wear and tear. To my knowledge, no fore and aft or up/down adjustment exists for Schwintek (or "cable") slides---only in and out adjustments (or calibrations) are possible.
