Under the influence of Covid lockdown, peer pressure and Mim's Kala closeout, I bought a cedar-top 8-string tenor. The G and C courses are octave pairs. This thing is a sound cannon. Cantankerous, beautiful, and difficult to handle. We have spent many interesting hours together. Sometimes we are locked in fierce dominance battles over issues such as a clean Bb chord. Other times we make beautiful music. My goal is to get better at predicting which it's gonna be.
I expected to use this mainly for fingerpicked chords to accompany vocals, and it is lovely. Except when it isn't. Sometimes there are, as the Emperor of Austria says in Amadeus, too many notes. Sometimes the uke sounds fine on its own, but I can't get my voice to blend. I was working on two folksongs in the key of G -- Dylan's Tomorrow is a Long Time and Tom Paxton's Last Thing on My Mind -- and we sounded great on Paxton and terrible on Dylan. Why? I have no idea.
I tried playing blues and it was too jangly. Except Mississippi John Hurt songs, which it was born to play. I was sure jazz chords in the Great American Songbook would sound dreadful and they do -- unless I strum lightly with the pads (no nails) of my fingers, in which case it sounds wonderful. Rock and country, well if it plays on a 12-string guitar then it's good on the 8-string. Lead guitar riffs and chord/melody? Probably not. If you want to hear individual notes, those octave strings will distract from the melody.
The upshot is, I would never consider an 8-string to be an all-purpose ukulele. IMHO it is a niche instrument -- and exactly which niche is something you will spend some time figuring out. You might need to experiment with different playing styles to make it work. I don't regret the Kala for a moment, it's fun having a uke I can argue with! But I wouldn't suggest anybody buy an 8-string until you've already found your best-buddy 4-string uke.