TOC only tickets should be binned. They're a scam. TOC gets it's tickets to the top of the machine by being 10p cheaper. Person gets smacked again for effectively twice the fare by the guard. TOC gets a slice of that if it's any permitted through ORCATS as well.
I do agree with this. Initially, there were no single TOC fares, they have just been introduced for commercial advantage to upstage Orcats, and are quite incompatible with open boarding. If made available it should be up to the TOC to find a way to check tickets before boarding. If that's too difficult, don't do them.
Contrary to the belief of many here, if a casual passenger sees fares for the same train offering for £10, £15 and £20, they will go for the £10 one. Doing T&Cs in railway-speak doesn't cut it. Many otherwise well-educated people I have spoken to find the ticket approach somewhat incomprehensible, and ticket machines which offer nonsenses (eg the first page of tickets to London at Worcester Shrub Hill ONLY offered me tickets on WMT via Birmingham) to be useless.