Two bars max and lack of project storage are probably the main downsides of MK1 machines, plus they are no longer serviced by Elektron and the PSUs are hard to find.
The UW capability is pretty fun, not essential and not the best as a sampler (your AR can probably do that better) but can do some pretty wild stuff with resampling, probably well suited to IDM vibes.
I’d definitely be tempted to look for an mk2, and decide on UW based on price. However if you found a really good bargain on an mk1, it would still be a great machine!