So today I received an IBM Options Model M15.

I'm going to be using it for the next couple of days to get a feel for it. It's really a lot funkier than I thought it would be so it's going to take me a some time to get acquainted with all of its features. I'll try to have a review of it posted some time this weekend. I'll be comparing it to a IBM F AT, 1395401, and an IBM SSK. I don't have an M2 to compare it to unfortunately so that one will have to wait for a bit.
Here are some size comparison photos:


But I have to say... I'm already really liking the thing.