Two slides in our 30" Cambria and wouldn't have purchased without them. As far as those frightened the slide may not retract it is similar to having power windows, what would you do if your window wouldn't go up in the pouring rain.At least the slide you can manually retract.
Use the locks that keep the slide from opening by itself, I had a weld break on the bracket that is attached to the retraction rail and the rear of the slide moved out a few inches at 65mph. The front lock, properly engaged, saved the day.
Maintenance: keep the rails clean and mildly lubed. When a slide is out it attracts dust/dirt and will slow the movement in/out.
The most important suggestion is look at coaches that fit YOUR needs. Sit in it with slides both open and closed. Tons of slides out there, tons of happy users.