The rooms at MStay 146 are decent-sized, clean, and modern. However, this was one of the most uncomfortable beds I've ever slept on -- horrid springs in the mattress. Additionally, the room was NOISY. On a busy street, you expect noise from outside, but because of the high ceilings and vinyl flooring, the rooms inside are noisy. We could hear every conversation the people staying in the room above us had, heard every scrape of chair, step of foot, heard them using the bathroom, opening drawers...
Our second night we discovered that our bed mattress was actually upside down -- the other side had a padded cover attached to it. We flipped the mattress, which helped some, but I still wouldn't rate this as a comfortable room.
Out of all the hotels I have stayed in London, this is my least favorite. Leonardo was kind and welcoming in the front office and the location is great, but I would not return as sleep is a necessity and it wasn't possible in this room.