Dexxter and Peppol subscription

Your recurring subscription is automatically renewed every year. That is the only difference.

And yes, you can register on the Peppol network with Dexxter. There is no additional cost.

If you choose a one-off subscription, are you then tied to Dexxter or can you still stop Dexxter?

If you opt for a one-off annual subscription, you pay 180 euros excl. VAT for 1 year of Dexxter. You are not really tied to it :) But you do purchase access to Dexxter for the coming year for that one-off amount.