i always use them on either a decent dog ml or a parlay....and if u push 1/2 the parlay of course u get paid ml on the other half, which stinks , cuz you lose the betting money and only get a little cash for it....but on a couple occasions i have pushed both sides of the parlay, and i got it back.....im sure every book differs
Typically no... and therefore you don't ever want to use a Bonus Play on an even spread...and you don't typically want to use Bonus Plays on spreads anyhow unless the juice is a very high positive (as in the case of some alternative spreads).