It'll be up in the air as to weather the new global upgrades are in the same boat... but lets consider a few things we know and what is on the table.

-The primary complaint about SWUs was having to put up a pile of cash and not having advance inventory to confirm, so having to go on the waitlist and the chance of sitting in the back on a 5k+ ticket. However, most often these cleared ahead of time or at least before going to the airport list.

-Delta removed the ability to view and get alerts for upgrade inventory, making it more difficult to use SWUs. Global certs would also apply here since it will be difficult to find what flights have upgrade availability.

Logical extrapolation would suggest that advance upgrade inventory for the globals will be tight and more difficult to use, since practically any DM in Y on an intl flight would be using one of these to try to get up front. The same complaint about absence of advance inventory will almost certainly be true with the new certs. The difference being, if you're stuck in the back you still only paid for your low bucket ticket and not an M. I can still see pax being upset because they try to use a cert but don't clear in advance and end up not clearing at the gate with an upgrade that list looks like a domestic flight.