Ok that looks similar to the silistretcher ADS. Yes, if you max pulled vacuum with the screw top that is way more vacuum then you need.
A quarter to half a turn should be all it takes to get a good hold on your glans. Also, try to eliminate as much vacant space in the bell cup as possible. Meaning, the inside of the screw should be as close to the entrance of the bell to where just your glans fits in. When you roll down the sleeve that is really what creates the main hold, and then the small reverse turn creates a good measure of vacuum keeping it all secure.
It will take some getting used to, and I would say start slow with wearing for an hour at a time and then checking and resetting if you think you can go for more. After a couple weeks, you will be able to work up to wearing it all day and only having to take it off for bathroom breaks.