I won't get into the whole should or shouldn't debate because there is no right answer. The only people that may find a right answer will be using their kits and either thankful to have the knife, or deeply regretting the decision not to.

A flat knife like the Jensen doesn't have to go into the tin though. It could be held on the outside with tape, ranger bands, paracord wrap, etc. The edge could be protected/guarded a lot of different ways but if a skeletal handled knife was chisel ground the edge could rest against the tin and be safe (much like the KISS knife).

Regarding the Jensen J.U.S.T. You may want to do some searchs over at BladeForums for Jensen Elite Blades. Jensen may be out of business, and he is definitely hard to reach all of a sudden. There is some grumbling about knives and money owed, so if you can get a hold of him do some research first. Getting another knife maker to make one for you may be your best bet.

The Douk Douk comes to mind as far as folders go. It is nice and flat, but I think the small is just a bit to long to fit into an Altoids tin diagonally.

http://www.geocities.com/Hollywood/Set/2292/doukdoukrev.htm

http://www.covecutlery.com/item.cfm?ItemsID=323

If you can swing the price, PJ Tomes makes some very flat folders that are supposed to be very strong. The one linked to below has Ti handles but I think I've seen stainless steel in the past.

http://www.tomesknives.com/model%201-F.htm

He has these little production pieces he designed. I've never seen one in person but two of them are very flat too. The D2 steel seems promising.

http://www.tomesknives.com/production.htm

Let us know what you decide. I've been trying to decide what to do in this regard for quite a while.