I use Cloak quite often, and it works for me.  However..... I don't have waterhemp to deal with.

When I use Cloak, I use 6 oz/acre.  I used to use 4 oz/acre, and it wasn't quite enough.   

Remember, Chlorimuron is a ALS chemistry. So, if you have Waterhemp that is ALS-resistant, that means you are relying on the Metribuzin in that product to control Waterhemp.   Cloak is 64.3% metribuzin,  so 2 oz/acre Cloak is applying 1.2 oz/acre Metribuzin.  How often do you apply 1-1.25 oz/acre Metribuzin?   

Unless he was recommending it in additional to other residual products, I'd say that pesticide applicator gave you some bad advice. Even so..... I still say he gave you bad advice.