Cash only! So visit the ATM before going...
Friendly staff, great bagels, and a nice selection of cream cheese. No line at around 8pm on a Tuesday night (but you may have to fight your way through the line queued up for the ice cream place a few doors down... it's probably some absurdly famous place I've never heard of, but WOW was it packed - and I assume that Fairmount is equally packed at around 8am).
I took four bagels to go - two onion, two plain (but was wishing I'd gone for the garlic when I saw them through the little window). We went with the onion this morning - super fresh, not at all as dense/chewy as bagels in the US typically are, and very tasty. Yup, this is another place I'd surely come back to if I lived in Montreal. Enjoy!