As a trader, do you feel safe using such exchanges that haven’t released theirs or should the more transparent ones be given preference?
As a trader, you shouldn't be naive that most of these CEXs are using almost the same strategy used by institutional banks to get their customer trust. The proof of reserves is just another strategy used by CEX so that their user can have more trust in the exchange in other to use it as storage which is not something every crypto enthusiast must do.
As a trader proof of reserves or not you shouldn't totally trust or feel safe with any CEX.