Windscreens don't seem to have a lot of effect, at least not for filtering the 'plosives out in the studio. It is a good idea to use an actual pop filter for vocals, particularly when using a condensor microphone. Not only does it filter pops, it also helps keep moisture from the singers mouth from getting into the microphone. To get an idea how this works, blow through a good quality pop filter and move your hand up and down on the other side. You'll notice that you don't feel the breath on your hand directly behind where you are blowing, it actually diverts the air downwards (keepin it away from the microphone).