I have used this location several times now and it has become my "first choice" for rentals when coming to Montreal.
First off, the prices here are really good and you actually get the same vehicles as you would with National. The difference is that National has a points reward program and an "elite" program where you can get your car without stopping at the counter. Regardless, I enjoy the lower price over saving a few minutes.
The cars here are well maintained and I haven't ever had an issue. In the winter I find that they could be cleaner but I'm sure washing cars when it's -3 out isn't easy.
The returns are super fast and you have a full receipt before you walk away from the car which I love. I hate it when you return a car and they email a receipt that is higher than it should be so the receipt at return is a big plus.
Enjoy!