Based on my own experience, I often seem to need a few days or weeks to warm up to a new instrument. There's always the initial excitement, which is then followed by some form of emotional sobering up, before the excitement will either return or remain absent. In case of my custom tenor it actually took me almost a year (where it mostly stayed in its case) to fall truly in love with it, and now it's one of the two ukes I would never consider letting go. I also went through a similar thing with the guitarlele, though much more quickly: excitement, reluctance, excitement, over the course of two weeks. Now that it's becoming more familiar, it grows on me very fast.
I've also noticed that my preferences for tone and size aren't always the same. I'm not sure what that depends on, but my solution for it is to have a soprano, a (now again) high-G tenor (plus a second one that doesn't need a case), and the guitarlele. This gives me three distinctive playing/sound experiences, so whatever sounds good to me on a given day or in a given week, that's what I'll play. No longer need a low-G uke since the Kanile'a GL6 covers that area for me.
I also had a Pono baritone that I loved, and that was a genuinely great instrument, but I felt the size needed more than four strings (hence the GL6; I loved the lower tones, but missed the higher ones, and I wanted to combine that), so I ended up selling it to someone who now loves it very much. I also let my Opio concert go because the size didn't do what I hoped it would for me. Likewise, after a year I sold my KoAloha LN pineapple because after an initial love affair, it didn't get played and I was relatively sure that I would not return to it. Was still hard, but I felt kind of uncomfortable having these sit around being unused when a) I could use the money on something that I would play and b) someone might really love them and let their voices be heard. I'm glad I didn't do that with the custom tenor, which really I wasn't ready for when I got it, but that is now a gem I am very grateful for. That fear of regret is sometimes a burden and sometimes beneficial.
You said you had the Nui for a few months. How much have you actively been playing on it? I'd say declare a week or two as your Nui Quality Time and play nothing but this instrument during the period. See how you feel at the end.