I changed from a Mondeo 2.5 Zetec S to the Cup... would I go back? Never!!!
The Mondeo was a great car, well put together, stacks of space, very tidy handling for a car that weighs 1,450 kgs.
Downsides for me...
No real "fun"... they have huge grip, thanks to the 225/40/18 tyres, but you have to behave like an imbecile to get it to move about a bit on normal roads, and that for me is where the fun is... playing with it.
Expensive tyres... I get 12k from a set on the Cup and theyre £40-50 each. go price up some 225/40/18, and work on 16-18k at best (heavy engine and lots of torque).
It was a HUGE family car, bigger than I needed... my wife has a Focus, and I wanted a laugh, hence the Cup.
Last downside... getting slaughtered by everything from VTS Saxos to old 1.3 106 Ralleyes... and that was with a V6 (which I think is about an extra 15-20 bhp over the diesel?).
Id say go for it if you really need the space, but if not, I reckon after 5-10,000 miles youll be wishing you hadnt.
Mark