Hehe I edited my post in the time you added yours

but yeah make it without loosing KI it should be more alike that:
for example on Goku you have perfect SSJ already at 5.000.000 soo maybe USSJ should be used few millions later about 8.000.000 then you can Ascend to USSJ by pressing TURBO+ASCEND and you get(SSJ-2x+USSJ3x=6x) 48.000.000PL but very slow!! When you get to 10.000.000PL then you can ascend to SSJ2 and get(SSJ-2x+SSJ1.5x=3x) 30.000.000PL but be even faster! but if you liked more USSJ you can return to SSJ and still press Turbo+Ascend to change into USSJ! Soo in the game playing as a Saiyan you could easily choose if you want to be fast or powerful!
EDIT: Yeah to other characters could be alike, Frieza 100% is good, but his transformations are pernament, soo should it just be at his last trans? Picollo transformed himself to giant in DB after swallowing Kami, but maybe not make him a giant, just gave him something different! Maybe his clothes, yeah make him slower but gave him more deffence for every attacks!
lol EDIT2:
maybe 3xPL wouldn't be soo good for USSJ because SSJ(2x)+SSJ2(1.5x)=3xPL and SSJ(2x)+USSJ(3x)=6x twice more... well maybe USSJ should just gave 2xPL soo then SSJ(2x)+USSJ(2x)=4xPL it would still be stronger than SSJ2, but it would work out better(of course if USSJ would make speed half of original because if speed wouldn't dramatically get down people would just use more PL option for sure)!