Having a slide in a TT, TC or fiver is a different ball game. I do not like them in class C's where there is no room for a header like there is in a fiver and some A's.
I would only get a slide if I absolutely needed to have more room for living space, period.
I only owned slide models that were seasonal site rvs not used over the road.
I never had a slide issue in the few I owned.
IMO, the idea is to limit issues in the field when you are going to experience a lot of downtime waiting for rv repairs and parts while on vacation. You are better off with less. If you do buy a slide model make sure you can fully use the rv in the 'IN' position.
Because normal rv things do not get done at the factory level you need to rely on a good dealer to do them.
If your dealer is not willing to take the time to tweak things up when a unit arrives at his dealership or prior to your walkthrough then you might have more problems with things in general.
A good dealer can lessen future problems, especially involving things that go in and out, have to seal, have fused motors with electrical wiring and have to align on adjustable tracks in order to function properly.
What I have seen with slides:
Some slides had wiring issues where the electrical wires became frayed.
Some slide motors are very difficult to replace , I would learn how its done before I bought one. 12v slide motors are inexpensive motors and have a tendency to quit performing on some models. There are different slide manufacturers.
I, as well as many other owners that have had them, would stay away from a slide that houses a kitchen. I do not like gas and electrical flex lines that connect things in a kitchen. Many owners had issues there.
Some slides tend to wear carpets and floors and those need to be replaced at times.
Best advice...listen to the mechanics that repair them not the salesman selling them. Doing that saved me thousands of dollars and a lot of potential down time.