We did one of those many years ago to Santander and enjoyed it. We've also done the Norway ones a few times too from Hull and always had a good time. We still take 3 and 4 day cruises now we're living in Cyprus as we're only 10 minutes drive from Limassol Port.
The one thing we like about the mini-cruises is your holiday starts the moment you step aboard. No hanging around an airport terminal for 2 hours before you get on the plane, then a few hours flight in front of you, a transfer - before eventually, you reach your destination.
On board ship, you can have unpacked, got your bearings, had a few drinks and a meal in one of the restaurants by that time
The outbound cruise was a breeze to Santander although we didn't get too much time off ship before we had to return for departure. The crossing back through the Bay of Biscay was definitely one to remember. A bit like driving over cobbled streets for a couple of hours!
One small tip: we've always found the air-conditioning is turned up to full notch on board ships, no matter where you are and sometimes public rooms and even the cabins can feel a little on the chilly side so take something warm - just in case. As for what to wear, the weather won't be much different from UK at that time of year. Just dress in layers so if you're lucky and find a nice sheltered spot, you may get down to a t-shirt!
Winter holidays are always the hardest to plan a wardrobe. You have to plan for every season...
Most of all - ENJOY!
Shell
Limassol, Cyprus