The Express works okay, but I agree, spring for 4K+. Some of the Android-based devices so have some additional features, such as click down to preview what is on other channels. These include Google TV, Amazon Fire, and ONN. Roku has about a 50% market share, so while there have been some recent Roku issues, I believe that Tablo is putting the most energy into Roku.
Personally, I don’t recommend the ONN. It functions well, but is a budget device and is missing some basic control buttons that I find frustrating.
Here is a review that I wrote a while ago: