Is the microphone worth using? Half the time I just find myself saying the words in my head
I don't know about the microphone exactly (can't get it to work), but I would strongly recommend at least saying the words out loud rather than in your head. You need to physically condition your mouth to be able to create the sounds of your target language, particularly if you currently only speak one language. Think of it like a work-out for your mouth and what you're trying to do is strengthen the muscles in your mouth.
I'm not using the microphone either, but like ijskarhu said, I constantly say all the sentences that I'm supposed to translate and stuff out loud (My sister already came into my room, asking WTF are you doing?.. :D). I think, too, that it's essential to not just learn how to understand a word, but how to pronounce it. I mean, that's why we learn other languages, right? To communicate - and to do that you need to be able to speak the language properly yourself.