Depending on how it's set up at the moment i.e what boost it's running you won't neccessarily see any 'bhp gains' as such, but really you need to take it to a tuner familiar with setting up your particular boost controller to get the best from it.
They can be 'mapped' to alter the boost characteristics i.e how it comes in /spikes/holds/peaks etc, and being 4 channel you can have 4 different boost/characteristics which may be handy for you if you don' want to run full power all of the time.
Hope this helps.