This "simple agreement" is one we have been using for the last couple of years with ODXG.
The reason it works is that ther is NO hidden agenda, we all know where we stand and as far as i am concerned Reputation and Ethics are much more important than "short term gains."
Also there is a less funding involved which probably makes it a bit easier, HOWEVER we all agree how funds will be split up at the end, and stick to our word.
With some other recent DX-expeditions, "Just because it is apparently 'legal' or 'contractual', doesn't make it right"