Well, they both use the same satellites and radio signals. It's the same electronics in different packaging. Speaking of packaging, the product you linked to

Well, they both use the same satellites and radio signals. It's the same electronics in different packaging. Speaking of packaging, the product you linked to is the buoyant version. Don't get that for hiking, it's significantly larger (physically) than the non-buoyant one. Confusingly, they are both called the "ResQLink 400".