The good overwhelmingly outweigh the bad here.
Good: Mathew was hands-off and allowed me to stay privately and peacefully, and the location has great transit available on both sides with subway entrances just a few blocks away from the building. The immediate area also has a few really solid restaurants and it doesn't take long to walk down to the the harbor. The kitchen is very compact and useful and the city water is drinkable, which may be a surprise for some Americans.
Some of the bad is out of the host's control: The neighbors on the floor are constantly slamming their doors at all hours of the night. Toronto as a city and some areas/buildings in Toronto in particular are not friendly with people renting on this app, so do not expect any assistance from the staff or to have use of any of the amenities the building offers its full time residents.
Additionally, I encourage you to be realistic about how small this studio is. However small you're imagining it, it is probably smaller than that. This is not a huge issue for travelers who are mostly going to be seeing the city anyway.
The bathroom is very nice, though the shower head is kind of cheap. I assume this is the stock shower head that comes with the guest unit and so I can not blame the host for this.