Comp wise it's up to the club for local trials. The Hampshire series have put 20" and 26" together this year and I'm riding my Inspired in the same class with no problems. I imagine it would be the same for other club trials but at National level you'd probably have to ride 'out of class' due to 24" not fitting into any of the official categories.
I still don't quite get what you're doing with the bikes once you've bought them... Are you splitting and selling on eBay? Sending them to Africa? Flogging them down the pub? Interesting concept but I don't get where the business is. And so long as you don't make an advert as annoying as the 'webuyanycar.com' ones you're doing better than them!!
I used to love the idea of those aluminium pressed monocoque type X-Tort frames! Geometry was terrible for trials but they looked sweet . But yeah, 24" trials is definitely reintroducing more fun back into what 'real trials' has progressed into.
That's all assuming that the mugger/chav/rapist/angry midget who's attacking you has had the very kind forethought to choose the anti-stab knife for his stabbing duties, which, lets be fair here, isn't all that likely.
"designed to work as normal in the kitchen but to be ineffective as a weapon." I call bullshit. It's a knife. It has a f**king sharp blade on it. How can that be considered ineffective as a weapon?