You can use what ever you want. Nothing stopping you from using the run of the mill stuff found at Wal Mart, in fact some use it too.
I use Acryl Blu as minimally as possible. You might want to read through my article on Perfect Seams, which I describe using styrene as my primary filler and turning to putties and other such stuff as a last resort.
Acryl Blu has wonderful feathering properties, dries fast and is easily sanded and polished...but if you can build without the need for any fillers, the better off your build will be in the end.
Develop your skill sets so you don't require any fillers...like my naked jug...which has now fillers used at all.
