I got a foil and jib for my 5.5 uni, so I could also sail it as a sloop sometimes. But, since the 5.5 jib is SO large, I also got a furler & modified that jib with vertical battens.
I haven't really sailed the 5.5 much as a sloop, primarily because I wasn't really used to being nice to crew (uni sailor for too long), also because I wasn't very good at sailing with a jib (uni sailor too long), and just when I started to like the idea of sailing a sloop-rigged boat, I ended up finding a really great N5.7.

Now, it seems like I've been sailing the 5.7 more than the 5.5uni. First I raced Ruffriders, then some off-the-beach regattas, the 5.7 became my "surf boat", and the uni is the "lake cat". But now the uni is upside down & stripped, waiting for some gelcoat on the bottom to make it shiny.

I have also tried the (5.5) bow foil on the 5.7, for two reasons :
1) I sail the 5.7 a lot singlehanded, so I like to be able to furl the 5.7 jib. But, the jib furler I have makes the jib seem too high, so by using the foil, I can keep the bottom of the jib at the same height as if I had regular wires, and still have a furler. I don't think anyone minds the extra weight I carry around with that foil, but they might.

2) Photos : I can more easily mount a waterproof camera on the foil, set to take pictures every minute or so. Got some great action shots of nephews & nieces on summer vacation going through the surf. Also a nice set of images while sailing on Lake Buchanan from Black Rock Park all the way the waterfall (bet I was the first to do that).

Anyway I guess the answer about a jib for the 5.5uni - yes, it works, but it makes it quite a different boat. When I got the joib, I only really considered one option - the std 5.5sloop jib plus foil. (for sale, if you're interested). In hindsight, there was another option I should have considered - getting a spinnaker for the uni (with or without a small self-tacking jib). i.e. making it kind of like a F17. Oh well.