Not sure what they’re referring to, but there are a number of warnings when you install an APK and you have to enable a setting to allow you to install an APK. It’s not challenging or restrictive, but a user who is unfamiliar might be discouraged from installing an app this way after seeing the warnings.
Approval voting sounds good.
One issue I see with the star system is that people tend to have preconceptions about star ratings. E.g. some people never rate 5 stars on principle or will rate something 3 stars without realizing that is a 60% rating. My point is I think you might see some weird skew in the results based on this.