YASSSS, DO it. I only buy digital Switch games cause I can't be bothered to lose them all, lol.
Ummmmmm. Well, yes in that you can play forever for free. No in that the game is pretty expensive to build a collection. That said, they give a lot more away these days just by playing, but it would be very hard to build a lot of good decks, you'd probably have to prioritize if you want to do really well.
But there are also lots of modes that are free all the time; including lots of single player stuff and Battlegrounds, Hearthstone's auto-battler, which is just one of the most fun things I've ever played. I play as much Battlegrounds as I do regular Hearthstone and fully support joining for that alone.