if you have all cars maxpro then yes all engines will be useless. but if not, then you can use engines for old cars.
Well... for me, All same. this prokits card is just like new engine (like i3 or V12 MPI). I still don't know if we can get this prokits card outside festival, but again i3 or V12 MPI there were a time not available in engine box, Finish Line Box, nor random box and even in Exclusive Deals. GL made Player to buy i3 via BMW i8 Coupe R&D.
this just like, I played Lamborghini Centenario R&D and BMW i8 Coupe R&D, TWICE, and still can't get it nor upgrade it maxpro