Many thanks Vince for the reply - I've sent a follow up to the "support" email address.
I don't understand why 7 filter positions is not the 'standard' on most filter wheels - most buy filter wheels because they are working with a mono CCD, so chances are that a buyer of a filter wheel / mono CCD will want to do RGB & NB imaging at some point......& if you shoot NB it is often nice to quickly grab some short exposure RGB data to obtain & overlay some nice star colours over the false colour nebula clouds, so 7 filter positions would be way more convenient.
Additionally, as automation progresses in the amateur astro world, more & more are going to be remote accessing / controlling their kit, or even setting it up for autonomous operation......where it might not be convenient to manually switch filter sets over from RGB to NB or vice versa.
The remote/autonomous users out there may be a relatively small subset currently, but I believe it is growing & will continue to as the controlling software & hardware becomes cheaper & easier over time.