There's masses of space up front, but, despite the Mustang's sizeable proportions, the two rear seats offer extremely limited space. Children and particularly short grown-ups will fit, but most adults will need to contort their bodies unnaturally to get seated. However, there is a bit more head room than you’ll find in the back of the Audi TT, while the Mustang’s long doors provide easier access than you’ll find in the TT or BMW 2 Series. Even so, an Audi A5 is considerably more comfortable.
It’s not all doom and gloom, though; the Mustang gets Isofix mounts in the rear, so two child seats will be secure back there. Good luck justifying it as a sensible family car, though.
Officially, the Mustang has a bigger boot than you get in its immediate rivals; there’s 408 litres of space with the rear seats in place and you can fold those seats down when you need to carry longer items. However, the narrow opening and high load lip make it difficult to load bulky items. Ultimately, despite having a smaller and shallower load bay, the TT coupé, with its hatchback boot, is actually more practical.