If it's not for their own use, whose use is it for? It's literally just for their use. They may promise that they won't use that backdoor for purposes that aren't for your benefit, but that's just their promise. And how do they define "for your benefit"?
How secure from other attackers that back door is is only one aspect. It's important (and important to remember the truism that "if there's a way to access it legally, there's a way to access it illegally"), but not the only issue. Even if we assume that hackers really can't get in that way, the backdoor and the data collection are still unacceptable to me.
