I have done both the Dharavi slum tour and the midnight bike tour with Reality and they were both great tours! All the guides are very knowledgable and the tours are well planned and don't feel too 'touristy'.
I went on their first midnight bike tour and it was the most fun, it's so great to be able to see Mumbai by night, you get a whole different perspective. I highly recommend this for everyone visiting Mumbai! Plus you get a delicious breakfast and they take you to a wonderful place to see the sunrise over Mumbai!