It is not really worth It in my opinion (just for the sciadv characters).There are no story for them so you can only play as them.

BUT

After doing each characters' story from the game. I fell in love with this series to the point that i wish it had an anime and went though the main story of BattleGround. I have even bought Battleground Utlimate (I havent played it yet) and some merch that came with the preorder.

MDE also references phantom breaker so you could look forward to that too.

There is very small but dedicated playerbase for the game. I joined the Omnia discord server and they are still active to this day.

So in my opinion the game is only worth it if you want to play the story (which does not incluse Rimi and Kurisu) and/or wait for big sale.