The lids of the Actifry™ 2 in 1 and the Actifry™ Family Size appear identical at first blush. They are certainly the same size.
They are not, however, interchangeable because of a slight design difference.
The difference is that the Family Size back hinges are placed slightly further apart, as you will see in the photo above (the Family Size is on the right);
The result is that the two lids won’t “lock in” when interchanged on either model, as seen below. You’re looking at a Family Size lid on a 2 in 1 machine. Push it back in all you want, it will just gently spring back out:
At the front, the two sticky-out, protruding bits are different on both lids. The 2 in 1’s bits are each one solid prong; the Family Size one’s are two-pronged.
But, as the prongs are just cosmetic and have no function — they don’t act as catches at the front, or anything — it’s the back plastic hinge latch difference that seems to make the two lids non-interchangeable.
* Actifry™ is a registered trademark of SEB, France.