My issue with the Pocket integration is that it's non-removeable - you get it whether you want it or not, and even if you remove the button from the toolbar, the code is still there within Firefox. You can't remove it like a plugin. To me, it adds another security problem that can only be fixed with an update of the whole browser, and you don't have the option not to have it.
But as I said, Mozilla were very up-front with the plans. They weren't with Looking Glass.
Which leads nicely into my thought - then why not make it a plugin? Why not have the browser ship with Pocket as a plugin, thereby giving users the option to completely remove it?
That's a good question and I think Mozilla simply intents to make Pocket something that people choose Firefox over Chrome for (atleast the vast majority of mainstream users). They're also heavily working on improving it's privacy impact, which is already fairly low if you don't use it at all.
But as I said, Mozilla were very up-front with the plans. They weren't with Looking Glass.