Been thinking about moving on from my cloud nine ergo Tkl because the keyboard is huge and still requires a reach when going for the mouse.
Are the thumb clusters with the UHK similar in function to those that come with keyboards like the Glove80/zsa/dygma boards in which they open new layers?
I am considering the UHK with thumb clusters and trackball.
Yes, in the sense you can use the thumb to trigger additional layers. No, in the sense that you have far less thumb keys than with other options. The latter can be seen as a disadvantage, because you have fewer keys. But the advantage is that you can place the thumb how you like it and not how the keyboard dictates it. I think 1 or max 2 thumb keys is the best for regular use. Additional keys, like the case keys in the UHK, can be handy, but are not that important IMO.
I use the left key (labeled as MOD) as such, while the right key (labeled as Space) is used as space, when tapped and acts as a MOD key when hold. That works perfect and I never have false triggers. For more layers I use the keys left and right of the home-row position, CapsLock-Position and '-key Position.