I'm wondering if it's even worth attempting to use one?

AMS-SIN & SIN-DPS share the same flight number, as do CDG-LAX & LAX-PPT, but presumably have different upgrade inventory since they're sold separately.

Has anyone felt crazy enough??

Given the problems with effectively using GUCs on AF or KL on married segments (directs are fine as you can see the exact fare class numbers there at the time of booking, so know you will be able to upgrade), I'm thinking towards giving this a miss even though either of these were always my dream GUC uses, going from PE to J.

However, if there were some way of cancelling the ticket within 24 hours - if the upgrade across married segments was not possible - like is possible with flights touching the US, I would jump on this in a heartbeat. Not sure whether or not that rule would apply to the AF routing since it doesn't depart from or arrive in the US. Sort of.