I think in the two quotes, either doesn't mean only one of the two options. Since these are product reviews, it makes no sense to say the first option is better than only one of the latter two options. They obviously want to recommend the best option. In the first quote, I think they want to say the round-faced watch seems bigger than each of the other two square watches. The two square watches both seem smaller than the round-faced watch. If so, can "each" be used instead?
Design-wise, the Moto 360 might first surprise because of its size – it seems bigger than either of the other two smartwatches because of its circular design, ... (TechCrunch)
For example, the Lumia 900 will net you $100 less than either of the other two phones. (TechCrunch)