I'm actually very interested in picking this up as a varietal to regularly play; the smaller chessboard size and reduced pieces would (theoretically) result in faster, pickup play.
5 X 5 is also really fun. It's the queen side basically, with a row of pawns in front. So there's only one row of open spaces between the two sides. It really stretches my brain to play it, but has helped me get better at calculation for sure.