I was intrigued by this Commodore 64 cartridge which had Datel Electronics moulded into the plastic housing and a single button on the top. I was thinking it could be an interesting Datel cartridge, possibly a Reset or Fastload cart pre-Action Replay era.
On the inside it appears to be an Evesham Micros cartridge. It's an 8kB ROM directly soldered to the PCB without a socket.
Here is the 8kB ROM dump if you need it:
Quick Disk Plus (Binary)
Quick Disk Plus (.crt) - VICE compatible crt image
I've seen a Softcell Quickdisk+ MkII advertised on eBay, manufactured in South Africa. I don't know if this ROM is a MkI or MkII variant, I couldn't see any obvious differences from the listing pictures.
The author appears to be Angus Ager who was responsible for other products sold by Evesham Micros, e.g. Freeze Frame. Presumably based in Barnet, Herts as the string appears in the ROM just after Softcell 1984.
