If you're worried about encryption, though, you wouldn't be using their app to display the pushed messages, you'd be using something you control; you only use their push infrastructure as infrastructure.
Pushover uses SSL, and then hands off to GCM for notifications. Yes, it's not end to end and you don't control the keys, but it seems to be the best current option and is MILES better than Pushbullet, who have yet to come up with a way to monetize.