sad thing is a prius ain't even that economical. Push it to a half decent speed and watch that mpg drop. My 2L diesel can match that doing over 70 mph.
5/5 last level is tough though. Just remember that recycling basic lasers gives back the amount to build them, shift the defences to give your self a good start!
And the lag kinda helps :)
I think its description should be
"A dice game of great luck (and a little skill)
But it is a nice little time waster tho. Could be expanded to include a campaign there you must battle around a map area.