Henchmen Heavy Bolter Spam

While looking at what could be the premise of the Upcoming Grey Knights codex I noticed that the use of Inquisitor Coteaz could allow someone to spam Heavy Bolters and Plasma Cannons like crazy. Today however I would just like to evaluate the points and see if it's worth doing?

In the New Grey Knight codex it appears we'll have the ability to take a heavy bolter on a BS 3 Servitor for all of 10 points. One hitch though, if an Inquisitor is not in the unit, the servitors do not work unless you can roll a 4+ each turn.

The Breakdown, in 6 turns we can assume it'll fire 3 times, with a hit rate of 4.5 so for ten points we'll be spending 2.2 points a hit.

A Space Marine Devastator with Heavy Bolter will run 32 points. It will fire all 6 turns and will have 12 hits through out the game at 2.66 points a hit.

We can see that it's possible for players to run a Heavy Bolter Servitor at a better cost for firepower then Space Marines. Will this be useful I do not know, but at least we know that they are not completely useless.