Personally I’ve heard very good things about mailbox.org

It can be paid anonymously, if you want. There is no (real) free option, and you didn’t mention if you were only looking at those, but your examples are mostly free.

70 W is very casual riding, like 15 km/h or so. Anyone actually training (20-25 km/h or simulating anything with hills) will be more in the 100-150 W range. My fridge uses 70 W as an example, and only when actively running, with a duty cycle of 40% or so. Obviously this isn’t an industrial fridge or freezer.