Well it's the first time I've seen one of those, but I'm not surprised it's Bob Howell producing it - he's very well-known in the community for making useful bit & pieces for the box, Auto Dil Valve, 4th Cell holder and HUD to name but three.
There are already a good few people diving with 7s bolted to their units in place of the 3s, using a 'Jan box' - see http://www.btinternet.com/~madmole/divemole.htm under modifications. Basically it gives you a load more on-board bailout gas but does make the unit very bulky. Great if you hate carrying slings though.
the bulk of a jan box is the least of your worrys i remember taking out a few members of the northern gas team who had these about 4 years ago,you'd need to have thighs like fatima witbread to lift the thing off the floor not to mention a front on profile like a garage door,great in a bit of tide!!!!!!!!!!!!!!
last i heard most of them have dumped the idea for side mounts