It doesn’t have any amplification so the maximum gain you can get is usually best. You get the maximum gain by setting to -10.
The FA Pro sticks have amplification so using the maximum gain you can get is NOT a good idea.
In some locations the LNA which is in front of the filter will overload due to interference, changing gain will not help you in this case only an additional filter will.
The Radarbox SDR has the filter first then the LNA so it handles interference better while losing some sensitivity.