Opera doesn't have the other concerns raised here. They aren't vendors of anything else themselves, and have no particular reason to use their data to further other goals they may have.
The question of whether this technically "works" is uninteresting. The answer is yes.
I would worry about Opera precisely because they aren't vendors of anything else themselves. Amazon can run these servers just to increase the cachet of the tablets they sell.
Opera needs to make sure that the servers they're running are bringing in income.
The question of whether this technically "works" is uninteresting. The answer is yes.