I am not sure I agree with Peg. Perhaps "hole in the wall" has changed its meaning over time... but since the 1980s (as long as I can remember) "hole in the wall" has meant ATM/cash machine - though it has admittedly declined in use.
I've never seen a "hole in the wall" serving food in the UK, and I've never heard that usage of the phrase in the UK. I remember being quite surprised when I moved to Canada three years ago to discover this alternate meaning for the phrase.
Just discovered this, I popped in for a quick dinner after work, around 6pm. Really impressed!
The place is pretty much as described by the OP, it's simple and down-to-earth, much like the streetside Thali restaurants in North India it aims to recreate. I spent some time in Gujarat in 2008, and with the traditional metal thali plates and cups, the complex aromatic flavours and authentic music playing, I was taken right back there!
The prices are incredible, quite possibly the cheapest you'll find in Montreal (on a par with the far inferior Indian buffet in the Eaton Centre food court). They're now 50c higher than those above but you will feel very full for $9+tax, with no waiting. A real bargain.
The reason this place is better is the flavours, you can tell that authentic recipes have been used. The butter chicken was creamy and succulent, the lamb curry had a great complex spicy flavour, and the saag was just right, smooth but still maintaining some texture. I agree with the previous commenter about the naan, beautifully fluffy and soft but still sturdy enough to scoop up the curries. Generally the spice level was about right, hotter than most North American indian restaurants but still softened slightly for the Western palette. Just below a madras in UK terms.
It was also nice to see the meat was good quality, no bones or fat (this is one area where it's better to take the Western approach than be authentic!)
All in all, thoroughly recommended. Well worth a visit.