Name clashes only matter if there is room for confusion in the mind of the consumer. As long as there's no other eBook reader with that name, they're OK. Trademarks are "sector specific" - eg you could register "Crispy-Bake" as a trademark for a cooking-related product, but it wouldn't stop someone releasing, say, a "Crispy-Bake" PC
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I would note, however, that "EZ Reader" isn't a very good name if it's intended to be sold world-wide. In most of the English-speaking world, the letter "Z" is pronounced "Zed", not "Zee", therefore "EZ" being a variant of "Easy" will not occur to most people seeing the name.