To start with the good: we love Montmartre and this accommodation is in the middle of it. Also, in an old fashioned way, the mattress we slept on was comfortable. Also, the shower water was hot! There's not much more good to be said however.
Check-in required retrieving the keys from a locksafe in a minimarket about 300m away. Thereafter the security was extraordinary for the unloved nature of what was being protected....street entrance required a code. Next entrance required a different code. Third door required a key and we were finally at the door to the accommodation, which of course required another key.
The apartment itself? Tired and tiny. Crammed with the owner's possessions.
To sum up? Suitable for a cheap night or two, except it isn't cheap. Then again, that's Paris.