I bought two of these. I'm deffo sold on the idea of not having to pay for a PolyTune function I never use anyway. So these do everything I need them too and come at a somewhat lower price. That said, overpriced they are all. They tune well, but workmanship-wise they are, well, seriously overpriced.
One of these has a very loose shoe to tuner swivel connection, meaning it moves about very easily. I use it on a guitar, so it's not too bad as it's not too far away; on one of my basses, fast access would come with the risk of actually moving it, rather than hitting the on button; or maybe that's my fault of having proportionally the correct arm length for my body size.
The second one doesn't deal well with basses (it's not the bass, I have four tuners and three basses, so have plenty of comparison). It actually tunes fine, but displays the wrong note, usually a fifth apart; i.e. it seems to pick up the route very well but the first overtone. It's not much of a biggie, coz you should be tuned-up beforehand and only need it for minor adjustments. It's just not acceptable at this price!
These UniTunes, whilst cheaper than the PolyTunes (and I never used that functionality, so welcome their simpler cousins) are not exactly cheap, so I'd expect them to live up to their price - at least a little.
But this has always been a problem with these tuners: good tuning features (bar that one UniTune), fast, but paired with cheap, nasty housing and cobbling together. On one of my 5-year old PolyTunes the housing rattles; and not only on basses but also guitars. Give it a tap and it'll stop for quite some time. But again, not at this price point!
SUMMARY: These are fast and accurate (usually), there's a reason why you see them on so many bass and guitar player's headstocks. But they a badly and carelessly cobbled together and somewhat awkward to use. Exchanging the battery should be a breeze, not a fiddle. The on-button is not in the greatest position if they're strapped to a bass, depending on where you have space to clip them. On a positive note, you can of course turn them around, to sit behind the headstock. The display will simply turn round for you.
I've not found better, so I have four of these (2x Uni, 2x Poly), they do outperform the rest. But, basically, they'll have to do until the real thing comes along.