Update on heatbed: I've been using it regularly to print ABS and it's been faultless. Kaptop tape on the metal and a small amount of ABS Juice wiped over with a tissue makes the prints stick every time.
Very pleased with it. I think I'll give up on PLA!
One question: could I run the printer without the fan on? I notice M107 Gcode has no effect, so I'm thinking of just unplugging it. Will it be OK? At the moment the fan ducts are shaped in a way that tape wont stick easily.