That's a good looking find - I was thinking of a raised pond of somekind, and was having 2nd thoughts - child safety (from a house selling point of view some point down the line) - this looks like a good solution.
I can't comment on stocking levels (10 sounds a bit high though)
Personally (unless one of the coldwater bods screams no loudly) I'd be tempted myself
They're certainly attractive, but I would be concerned about the depth. 60cm is definitely not enough, especially as it's all above ground and even 80cm is less than the recommended minimum depth by 10cm.
I think the shop assistant is being very optimistic if he's saying you can put 10 fish in it. The coldwater tank size guide advises 180 litres plus 55 per additional fish for common goldfish. So that's 5 at the most! Plus they're only 1 metre wide where common goldies need at least 4 feet (122cm)swimming length.