RTMs are the best when you know where the enemy is, or is going to be. Heroes are especially easy to kill with a perfectly thrown and triggered RTM. Its almost too easy... BB is good for RTMs if youre on MI6 becuase you know that's where the enemy is heading and you do significant damage to the box too.
Proxies are new to me... Ive been using RTMs for so long, which are usually reserved for hero kills, I forget I have them most of the time. They do help you hold an area and even if the enemy spots them or survives you get a bit of a warning because the report is so distinct.