You don’t say exactly where your stops are in Europe, but normally, the b2b’s are treated just like any port stop. However, that can change, depending on the local customs.
We did a b2b which was 16 nights and a stop in Barcelona BCN, then another 7 nights.
To our surprise, customs BCN wanted a cleared ship and b2b’s had to clear last. Don’t know why, but they were not very efficient at it, took us longer than usual. So, unlikely, but always a possibility.
It doesn’t matter if you are booked as 1 cruise or a b2b, you still clear, if they tell you too.
We look at the price, the stock OBC and availability of cabins.
Compare all and see what’s best for you.
If booked as 1 cruise, you pay one fee of $14.99 OceanNow fee instead of 2 charges of $14.99. If you have Plus/Premier package, then doesn’t matter, it’s included.