Bought an Isla 700

In the end I didn't buy a second hand bike for my son. We went for new.
It arrived quickly in a big cardboard box and seems good. Screw the pedals in, straighten the handlebars and away.
It's a bit of an extravagance really because my son (aged 11) has only just started Cyclocross at a very fun level.

It was a success on the first competition as the course was longer than the first course he competed on. His little Trek mountain bike wouldn't have got up to speed I don't think and he was reluctant to change gear on the Trek as it was a bit clunky.

It's not the lightest of bikes but it's ok. I feel a bit guilty that he has to have a bike that is twice as heavy as mine, but it'll do him good I'm sure.
The cantilever brakes are good and strong with lot's of clearance for the muck. I put on a pair of magic pro wheels that I had made with Shimano 105 hubs. They're a bit lighter and better than the wheels that came with the bike, but not too much lighter. I did splash out on some nice cross tyres though from Chain Reaction.