Thanks Vin appreciate your help.
I agree that standalone poller upgrades are more straight forward because you just have to match the primary poller (NPM, SAM or whatever) version and then choose the right additional poller version.
Using the bundle, the necessary information: which module pollers have been updated in the bundle release is completely missing.
So how should a customer know if this upgrade is necessary / recommended for them...
Ironically the Customer Portal Releasnotes Link to Additional Polling Engine points to the normal NPM Release Notes and there is no single word about Additional Pollers.
I will open a ticket...