I was going to buy a Harmony One way back, but my Harmony 880 was still working fine, so I didn't. I should have. Or two. Or three.
I've fixed at least three buttons on my Harmony 880, putting in little spacers so that the contact point gets pressed a little harder. I've also re-soldered on the USB port twice, and the second time reinforced the mounting. Plus improved the contacts on the remote so that it always connects and charges on the base station without wiggling, which was a common complaint. I'm even still on the original rechargeable battery!
Get on it Hendrik, you can fix your old Harmony One if you still have it! Or maybe there are
second-hand ones around that still work?
On the issue of alternatives, there aren't any that support the Activities Based use, as far as I know, and I really love that paradigm. I'm pretty sure the Harmony patented the approach, so now Logitech owns it. The current line does look pretty bad. I think you have the best choice now with the 350. The 650 doesn't seem to add much. I don't want a hub, or whole house control, particularly Logitech's. I just want a better IR or wireless remote when the 880 finally dies.
There are still some Harmony Ultimate One remotes on sale in Australia, but from memory, they were not as good as the original Harmony One. No number buttons!
So sorry, no recommendations from me.