I had to play B + N over the board early in my career, so it's definitely YMMV. It takes very little study: For B + N knowing that you mate in the corner that matches the color of the bishop, and that the knight needs to 'lead' in the effort to corral the king is all you really need to know. A half day of practice would cement it, I suspect.

I think bishop+knight endgame could be much more common if players actually tried to get them when defending after exchanges of queens and rooks. So, exchange as many pawns as possible and maybe sacrifice a piece for a couple of last pawns and here your opponent goes.

Also, if memory servers me I've seen two grandmaster games only during this week, where this endgame could happen, but the players didn't want their opponents to show the technique. One of these games was yesterday: https://www.chessbomb.com/arena/2020-russian-championship-su...

But indeed, rook endgames are way much more important from a practical point of view.