I've had campers with and without slide outs. We've had zero issues with any of them, and we're had all three types of slider mechanisms. We do keep them lubed, including the seal flaps, and have our local mobile RV tech check everything out at least every couple of years.
The smallest trailer (no slides) was great for overnight stays, and since it was our first one, we didn't realize what we would be missing. But I can tell you that moving around in that cramped space was not a lot of fun. I think it heightened frustrations and led to us using it less and less over time.
Our second trailer was the same length as the first one, but had a small slide out for the dinette, which opened up the kitchen area (directly across from it) and allowed us to actually pass each other without one of us having to sit in the dinette. It was much better, but there was no way to sit anywhere other than the very small (and tight) dinette booth. Could not even use a folding chair in the aisle without completely blocking access to the restroom.
So we replaced that one with a much larger (34' 8" long!) 5th wheel with three slides: bedroom, and two across from each other in the living area. One contained just the sleeper sofa. The other was much larger (probably 18 feet long), and included the dining table as well as the rocker/recliners. The mechanism was hydraulic and was quite trouble-free, other than a circuit breaker that would trip every 10 seconds or so while extending or retracting the slides. It turned out there was a wire connecting to the hydraulic pump that was only finger-tight. Once we tightened that connection, it was completely trouble free.
We loved the 5er when we went places where we stayed for a week to 10 days at a time. It towed much more nicely than the bumper-pull, and was like home away from home once we arrived and got set up. But that 34 footer was a much bigger PITA to park, and set up/take down was a lot more of a chore (no auto-levelers). We do a lot of trips where we go somewhere for two or nights, sightseeing during the non-traveling days, and those are often single-day stops. And as we got older, all the bending and crawling underneath became harder and harder. Plus, my wife could not (or would not) drive the truck+5er combo, so it was all on my shoulders. This came to a head when I got sick (really bad flu) the morning we were supposed to check out of the campground. Luckily, the CG was able to extend our stay, and we didn't even have to move to another site, but it scared the you-know-what out of my wife. She realized that if anything happened to me while we were on the road, it would not be pretty...
So we sold the 5er, and purchased a 25' Jayco Redhawk SE 22C, with a single Schintek slide out for the queen bed itself. That slide allows us room to walk around the bed on three sides (no climbing over each other in the middle of the night), and allows the bathroom to be much larger – enough so that I can comfortably take a shower and get dressed in the bathroom. The slide itself extends only about 2 feet, so it's not very obtrusive.
This MH is small enough that my wife is actually fairly comfortable driving it (and will get more comfortable over time as she drives more). The floor plan gives us enough interior room that we won't want to kill each other when we stay somewhere for a few days, or get stuck inside for a few rainy days... We are looking forward to being able to go a lot of places our larger rigs simply could not go. For now, we're not planning on using a TOAD, but are taking a pair of e-bikes with us for getting around the campground. We're going to try it for a while without any auto-levelers, but have agreed that if we decide we want them, we will add them later.
At this point, I would not even consider a camper that didn't have a slide out. Like others have mentioned, I'm more partial to the smaller slide outs, and am still just a bit leery of those "full-wall" sliders.
