I've been using Channels for only a few months, and here's some random feedback, some of which is a result of having been a long-time TiVo user.
Search could be more useful.
I have a custom record pass for "Bing Crosby", but if I do a search for "Bing Crosby" in the Search tab, no results.
At least, I think it's no results. There's just a blank screen, no "no results found" or "this only searches titles" or any info that might be helpful.
No way to browse by Pass. If I want to find all the movies that my Bing Crosby pass recorded, good luck. They're mixed in with all the other movies.
No way to view a channel by itself. I'd love to just look at the Hallmark channel and see what cheesy holiday movies I haven't seen yet, but I have to swipe through the timeline, swipe, swipe, swipe, seemingly forever. On the TiVo iPad app, I can tap on the station name and it shows me the upcoming schedule for that channel. (Yes, I've used the "premiered in 2020 holiday" pass that someone posted on the forums a while ago. It's great!)
Unhelpful and truncated error messages. I don't have a screenshot, but when the HDHomeRun has troubles, or when the URL for a TVE station changes, the error message is like "Unable to play station from http://cdn.ha…" and that's it. Despite the screen being large, the error message doesn't wrap, which is very frustrating.
Overall, I love Channels. I've been moving all my TiVo season passes over, since my 8-year-old Roamio Pro will die at some point, and I won't be getting a new TiVo due to their advertisements, etc. Channels is looking to be an excellent upgrade.