

I share your concerns about trust. With flatpaks we can still read the source and commits, but not many will or can do this every time they install and update software anyway. In this sense, we have little choice but to trust the verified developer and the community, who may of course be compromised too, regardless of distribution method. I suppose with flatpaks we have to check permissions and make them as restrictive as possible.
My understanding is that sandboxing is not mandatory for Snaps, but it is for flatpaks. Some of the Snap code not being open source, and generally the technology being centralised around Canonical apparently is off-putting for some.