A four-string electric bass and a five-string electric bass (or a six for that matter) are different instruments.
A five is usually a bit bigger obviously in the neck and fingerboard, requires a different muting technique than a four, may be much harder for guys who anchor their right hand thumb to reach across five instead of four, and really require a little more amp and cab to push the occasional low C's and D's realistically on a big stage. Anybody that tells you 'it's just a bass with an extra string' may be factually accurate in a small way, but otherwise that's BS: They're two different animals.
So it's enough different from a four-string (at first until you live with it long enough for it NOT to feel different) that it is a bit disconcerting at first. You can tell yourself all day long that it's still the same four strings, they just 'moved down' one string, but you just have to put in the time to make the mental jump.
That is, only if you want to make the mental jump.
I'd buy one IF what I see as advantages are also advantages to you (far easier transposition, playing more 'across' the fingerboard and less vertically, 'up and down' the fingerboard, and the occasional tasty low notes), and/or you feel drawn enough to get one and put in the time.
If not, find a nice four string that's an upgrade and get it. There's no implied test of musical manhood by playing 'more strings', though you'd think that reading any number of 'Should I Get a Five' posts here in TB.
The only good answer when it comes to buying anything new (or new to you) is 'Does This Help Me Make My Best Music?' What works best for you is the right answer, and if a four suits you best, there you go.
I converted to fives in the late 80's and never looked back, because it suited much better the way I wanted to see and address the fingerboard, I always felt out of place on a four-string, something was missing for me. That was the right answer for me, and I'd urge you to simply find the right answer for you, whatever that ultimately turns out to be.