It's a lot thicker on the sides, and on the back it's flat - so where as the Apple leather case has the hump for the camera, the Sena case is completely flat in the back. Imo, it is a noticeable size increase to the phone.
Granted, this provides a lot more protection but I find the Apple cases a lot thinner on an already massive phone. So I'm really torn. (Sena makes the phone feel big).
I went and got an Apple Silicon cuz I love how thin it feels - picking up from the desk is just amazing. This may be the first year I don't use a leather case.
What I found interesting was the noticeable number of Apple 12 leather case returns (even for the Pro Max) at my local Best Buy. Not sure if it was the popping out issue some have reported or what...
I'm really happy with my Green Apple Silicon. That dark green is ... perfect.