Why should/shouldn't I buy this?

Other half wants to buy one of these. She's adamant she's getting a Merc and won't be talked out of it (managed to talk her out of an Evoque, thank god) so I want to know what I'm getting myself into.

Above is an example but will likely be a C class couple (likely petrol). Could probably be convinced to look at other Mercs if theres any recommendations?

Any issues with these, what's engine like? Auto box ok?

Any and all opinions welcome, thanks in advance!