Hi Thom,
I am one of the few here who have actual real experience with the Jonah D100 housing. Keep in mind this is a different housing than the one for the Canon 10D.
If you haven't already read the review:
http://www.wetpixel.com/reviews/d100_jonah/The thing is, I didn't get to dive the housing - I carried it out on the boat, Craig and I played with it on the camera table, and then the boat turned around due to a tropical storm...:-( So I can't say how the housing would perform after multiple dives...
One thing I can say is that the 8" dome was not loose. That was someone elses comment about the 10D housing... The buttons on the D100 housing all made contact with the buttons on the camera for the unit I tested.
This housing is a lot smaller and lighter than the Aquatica and the Ikelite - it's made specifically to fit the D100:

If you'll look at the comparison shots in the review you can see that it's REALLY small - even smaller than the Nexus - which IMO is the benchmark Aluminum housing for the D100.
According to Prof Kim of Jonah, they have a new generation of housings coming out soon that have a different button design. Dr. Kim has also informed me that they have changed the handles to accept strobe mounts from popular American and Canadian manufacturers, as well as adding a lens release button to the front of the housing. I'm looking forward to trying one of these out in the future.
Cheers
James