Having read the answers given here I have to assume none of you have owned one.
700cc ones avoid, engine goes pop at less then 50K, about a 1K to fix, on the other hand if priced right it satill makes sense as cheap car.
800cc ones much better, both these earlier versions are good on fuel, and will get what the book says.
The newer 451's (07 0n for petrol and 09 on for diesel) with the 1000cc jap engine are reliable but not so good on fuel, 35 to 50 mpg depending on how they are driven, and Turbo or not.
The 800cc diesel (still a merc engine) is better on fuel, but not book figures, mine gets 65 ish to the gallon around town, 75 plus on a run, with free road tax.
Only had one fault, gearbox related that was sorted free of charge, after the warrenty had run out.
Check this forum for more info
Smartz
Neil.