Unit size on the Welsh course
I'd like commend the Welsh team on not making any of their units horrendously large. There are no units with more than seven lessons and, for me at least, this definitely helps with motivation; too many times have I felt put off from progressing through a tree on Duolingo because the next unit was nine or ten lessons long. I'd much rather have more units each with fewer lessons than vice versa. I don't know whether this was a conscious decision on the team's part but I'm glad the course ended up being structured this way in any case.
I always prefered the longer lessons where each word was tested three or four times across fifteen or twenty questions, but I can see why the decision was made. This way, those who learn a lot faster than me and don't need the repetition can move more quickly through the material. After all, there's nothing stopping me repeating a unit if I feel the need to go over the material more thoroughly.