@Der_Ryan_M you are wright about the different gaining of fast trainers but approximatly the gaining is the same.
I dont believe that 10-20 restpacks is big difference.
I think that would be very handy to know how many rests and how high your players skill will be after a drill.
Imagine that you bye one 3* FT and after using the calculator you know how much restpacks needed
and how high your skills will be after a drill.