Is a pop filter necessary?
Pop filters are necessary for anything voice related. It helps with sounds such as 'P' and 'B'; This is called plosives. Plosives is extra air going onto the microphone causeing a very annoying heavy breath/bass sound. If you care about audio quality and you want to be great at what you do, get a pop filter.
Which is better windscreen or pop filter?
Pop screens are much more effective against pop noises than windscreens. The latter also attenuate the treble response to some degree, while pop screens affect the sound far less. For optimal protection, the pop screen shouldn't be too close to the mic.
Can I use 2 pop filters?
For some singers and voice-over artists, 2 pop filters are the secret to making their performances completely balanced and flawless. So, yes, you can use 2 pop filters, and, depending on the case, you should at least try it.