A group of boomerang throwers with the 3-1-0 upgrades (Glave Ricochet and Faster Throwing) can be used for crowd control and easly dominate most non-M.O.A.B. class bloons with the help of a 0-2-0 monkey village.
A boomerang thrower with the 0-1-4 upgrades (Faster Throwing and M.O.A.B. Press) can be used to delay a M.O.A.B. B.F.B. or Z.O.M.G. bloon for a short time.
Although the upgrade description claims that the Boomerang Monkey shoots 20% faster with this upgrade, it actually shoots 33.3% faster. The 20% number is actually the amount the cooldown is reduced by.