Jim's place is a bit of a squeeze, but the photos and descriptions already tell you that, and the size is about as standard as any other Hong Kong accommodation of that price range. If you are quite crafty with spatial organisation and maximising space, you shouldn't have any problem at all.
Jim and his team, Alex and Margaret, were really wonderful and helpful. (maybe it helps that we speak Cantonese?)
Jim provided very clear directions on how to get from the airport to his place. As soon as we settled in, he and Alex gave us plenty of tips on what's worth seeing, and how to get around the city. It was also really convenient to have the street market only a street away, and plenty of 7 Elevens all around.
The room itself is tidy and clean. There's very little room to stand around, so it was a lot of sitting on our beds to work or read or snack. It comes with A/C, windows for natural light and ventilation, and a fan if you prefer to lower your energy footprint. The bathroom can be a bit too cramped for some people, but it suited my family fine. Just need to always remember to take out the toilet paper before showering, or hide it above the cabinet so it doesn't get wet!
When we left to catch the airport bus on our last day, Jim even helped carry our suitcase over to the bus stop! We were literally walking through the usual heavy Mong Kok crowd when he suddenly appeared. Apparently he needed to take a breather outside--whatever it was, it was a really nice finishing touch from him.
A lot of other places from the same price range are located in the Chungking Mansion area, which is a lot more stifling compared to the Mong Kok streets here. Furthermore, Jim and Co really add a personal and friendly touch to the stay.