I like both, depending on their use. For sociability, the swivel are great. For writing or some other, more 'stationary' function, the stationary are it. The swivel is too much work to keep it stationary!

I have lived in two places with breakfast bars in American style kitchens. I found that I tended to spend a great deal of time sitting there so a bar stool with a comfortable back is important. I made mine from pine, copied from some I saw in a bar. I was also given an old captains swivel seat from a yacht so I built a stand for it, reupholstered it and unfortunately left it for the new tenant who liked it. That was one of my favourite seats, to sit in comfort at a breakfast bar rather than balancing without a back to lean on.

If you want the seats to swing out from the island be sure to check that the island is substantial enough to take the load, also that the island is well anchored to the floor. If you consider the arm is for example 2 feet long, then sitting on the extende seat will be the same as applying your full weight to a crowbar, two people sitting on one side would destroy a normally constructed island. Similarly, if fitted to a wall make sure that they are anchored well and that the wall structure is suitable. A nice idea to save space though

Out of all the ones you’ve listed I like the one from Perch and Parrow but I’m confused when you say footprint within 48x48cm and this one is listed as 42x42cm. Incidentally I found them cheaper here: https://www.costco.co.uk/Furniture-Home/Dining-Room-Furniture/Chairs-Bar-Stools/Gallery-Palmer-Brown-Faux-Leather-Bar-Stool-2-Pack/p/263151 Also found this one: https://www.wayfair.co.uk/furniture/pdp/selsey-living-hoker-65cm-bar-stool-tcdv2652.html?piid= And a bit of a wild card but the cantilever might make it extra comfy: https://www.argos.co.uk/product/8835576 Also have a browse in the Houzz shop. They have lots of barstools so you may find something there.