First of all, Jack is a great host. If you ever need anything simply text him and you will get a helpful response in no time. Check-In and Check-Out were completely hassle-free, as he picked me up right from the door of the taxi.
The location of the apartment is right in the heart of Mong Kok and there will always be people on the streets. A supermarket is only 50m away and the MTR is only 1-2 mins away which is super convenient for Hong Kong.
You will share the washing machine with 4 other rooms, but this usually does not lead to any problems.
The room itself feels rather small at the beginning, but you will get used to it very fast, as this is simply how rooms in Mong Kok look like.
Overall very pleasant stay and I would come back!