Apparently there are equivalent products available for a similar sort of price range such as these RC Relays.

All mine would be is a smaller solid state version for a similar price with maybe a few extra features, so the market for custom controllers seems to be substantially smaller than I originally thought.. They'd be useful in Beetleweighs and Featherweights which are pushed for space, but unfortunately I can't see enough need for it to be worth getting a professional print run done, unless anyone can think of a suitable application?