I played fours exclusively for years, but bought my first five in 2008, and while I prefer playing fours most of the time, fives are darned useful. For example, I've played a couple of musicals, and a five was almost essential for both. And for the second one, having an active five (M-2500) was a plus.
In fact, I wish I'd bought a five earlier, because I was in a band with a songwriter who often composed in E flat and D. I got by with a drop tuner, which I liked for the tracks in D, but for E flat and some other keys a five is much better IMO. For example, when playing in B flat it's nice to have E flat easily accessible on the B string in a position consistent with standard tuning.
I haven't had any trouble switching between fours and fives either, provided I do so regularly. I hit a snag once after I'd been playing my five exclusively for months, and found the four disorienting for a few seconds.
I agree with others that you should take care when selecting a five, because scale length, string spacing, etc. make a huge difference in feel. I play mostly with a pick (due to a finger joint problem), so narrow string spacing is important to me. A relatively flat fretboard is also essential for me on a five.