눉I have been to Helsinki - one of my favorite cities - numerous times, and have stayed in all sorts of accommodations. This was among the worst.
Don't be misled by the pictures: the apartment is run-down, dingy, and in desperate need of both a (real) renovation and a deep cleaning. (The air vents, for example, are caked with dust and grime, the bathroom sink is "repaired" with duct tape, there are stains on the walls, etc., etc., etc.) I have stayed at Helsinki hostels in the past that were much nicer.
Apartment is located in a convenient but utterly charmless neighborhood, on busy street (much traffic, and a tram which runs directly below); with the windows open, it is not quiet. The next door neighbor is a cellist, and due to the paper-thin walls, you will feel as if s/he is in the apartment with you.
I must also add that the manager is, without question, the rudest "host" I have ever encountered, and apparently feels that she is doing you a favor by allowing you to stay here. Her rudeness only abated when she understood that I was keeping a record to share with booking.com.
Look a little further; for what you pay, you can do much, much better.
눇Not a disaster, but there are far, far better places to stay in Helsinki.
The woman who came to pick up the keys at checkout, and the local contact were both very pleasant and helpful.