Most online books are closer to 5% than 10% but yes.
The idea is that, at worst, you lose the vig but you can win both bets at the same time.
So if you bet $100 on each side you're guaranteed to get $195 back on your $200 investment. If the game lands on a 4 or a 7 you get $295 on your $200 (1 win, 1 push). And if it ends on 5 or 6 you get $390 on your $200.
You have to decide if the probabilities work out to make that a +EV wager, but usually if you're getting 2 "middle" points in a single-digit spread its gonna be worth it.
Would be way better if you had +7.5 and -5.5 though given the propensity for games to end on multiples of 7.