A diverter valve will generally be better than a dump valve.
When the dump valve operates the excess boost in the inlet manifold caused by the throttle closing is vented to atmosphere, this is bad for two reasons, firstly the turbo has just done all that work and you are ditching it into the atmosphere nad its better to use some of it by adding it back to the compressor inlt. Secondly, the MAF sensor has measured fuel for that air, so if it just disapears the ECU is lost as to how much air is in the inlet system and gets the fueling wrong. Not good.
The diverter valve just moves the air from after the turbo to before the turbo, therebuy not confusing the MAF sensor.
I hope that made sense....