The back to back could be a very practical idea- for families/groups of 4 they can face each other which would be nice.
Although I imagine for people you don't know it would be slightly awkward depending on how close the seats are hah.
I think another (family) coaster is what chessington has needed for a while to divert demand from rattlesnake/dragons fury/vampire so great to see this sort of investment happening, with an IP that parents (and grandparents) will also recognise. Given the jumanji brand has been around since 1995, I imagine it'll stay relevant for a good while yet.