Tom I've fitted couple hundred Chinese Prox switches and had probably less than 12 faulty ones. At just over £1 each they cannot be beaten by any Switch for the money. Don't use Omron but I'm pretty sure they will be quite bit more than £1. . . .You wasn't trying to use them with 5V was you.?

Regards Controller you get what you pay for I'm afraid and I cringe when I see people say they bought cheap chinese controller. EVERY motion controller for Mach is only as good the Plugin that runs it and NO Chinese controller is supported by Artsoft so your onto loser from the start.
But can tell you decent Motion controller has the same if not more impact than going from Analog to Digiital drives. Combine the two and you have Huge improvement of PP and Analog.

Cslabs are my first choice but you won't go wrong with Pokeys 57CNC or UC300/UC100 if on budget.