No ads, non-profit, contribute to research, etc. It also allows you to find out what others have spotted in your area. I like the range maps, the images across seasons, and other seasonal information.
The actual ML-based recognition is somewhat hidden, I think that part of the UI needs some work; it seems like it was made for researchers first then hacked for non-experts to use.
Seek is 220MB...
[1] https://besjournals.onlinelibrary.wiley.com/doi/10.1111/2041...
I just gave them a try for some common trees around Costa Rica that I'm confident in identifying, and they both did very well, slightly better than PictureThis and iNaturalist, which I've been using for a while.