A small update. Thanks to @Herr Tubthumper's considerable efforts, the kit arrived.
We've been using it for half a day and it only bloody works!
The app let's us see when the cat comes in - or is denied entry!
If you use NSC with any regularity then chip in a few quid (it's the best entertainment value you can get) or "pay" by living with the ads. It is a choice.
Of course the ads shouldn't ruin the experience, but they are intrusive - compared to no ads - for a reason. They want to get noticed and...
These guys could literally put a bullet in someone and their lunatic followers would find a way to see it as acceptable. Debate is pointless. It beggars belief.