We came to Montreal to celebrate our honeymoon and stayed in Serge's awesome apartment.
First, the location is amazing. You are right in the heart of the plateau, down the street from Schwartz's (you have to go) and easy walking distance to Mount Royal, everything in Mile End, and even Downtown. We were new to the city and without gps or maps, but we never felt unsafe wondering around near the apartment at any hour of the day.
Second, the apartment itself is very large and clean. There's a small kitchen with a minifridge, an AC unit, and great natural light. Even though you're in a really bustling neighborhood, we never had issues with noise. The AC worked great, but the weather was so nice while we were there it didn't make a huge difference (August).
Third, Serge is amazing. He was very easy to communicate with (we only speak English) and he had lots of great tips for places to. We loved everything he recommended and he keeps a little book where guests can write down what they did. We loved that too.
If you're looking for a good home base to explore Montreal, this is your spot. There might be spots that are a little closer to the subway system, but we ended up walking everywhere and loving it.