I thought about it and found them all ludicrously over priced for the usage one would encounter. In my view both O2 and Samsung.
I placed my money and my order for a Gear S with an independent outlet a while back. Each week Samsung and/or the outlet delays by another week but now indefinite delays. I thought Gear S would be a nice to have but Samsung total disregard for their customers is turning me off the brand.
Also in a couple of months when there is little shortage the product will be selling way beyond these inflated levels. I cannot understand why Amazon UK sells it for 380 pounds while Amazon US sells it for 380 dollars. So basically UK customers 55 % more for same product manufactures abroad than their American cousins. Makes little sense but explains Samsung and their resellers callous treatment of UK consumers. Whatever sums you do the 55pct increase does not add up.
My opinion is don't take any of the plans yet... Wait until after Xmas.