Wish you luck.
It seems to be the very same swap as the revised Boomerang -- except you tell them which block to use, making it even more restricted.
I myself do better with paper piecing for most blocks as ones with many pieces end up wonky...as you said, to each their own.
I wish the mail tracking requirement wasn't part of the rules...how would we get this to be revisited and revised?
Each person that mails a F8 or finished block should know up front that you are at the mercy of the mailing gremlins and take that chance at your own risk and agreement. I have a feeling that larger envelopes (containing all of your blocks) will be missing more easily than a small one will. (containing only 1 block).
Again good luck and best wishes.