As for the submission of data, the same could be said for all search engines. A browser is a communication tool, it sends data around. What we need to make sure is that it sends only the data you consent and only when/if you want.
Now, lets do a little exercise because you might know more then me about alternatives and I am using this thread to learn new things. If we want a "read it later" feature and we can't build our own, what solution you'd rather have instead of pocket? Is there any other service that you're more comfortable with? If you're not using Pocket and it is not sending any data because you're not using it, having that feature present is actually harming you?