I just had a great experience at this place. We were also arriving late - 11 pm - so I emailed them to let them know - they emailed back to say they would be waiting, and they were.
They directed us a few metres down the road, to a funky little studio apartment - self-contained with full kitchen (including coffee, tea, etc.). We spent two nights there - and we had a great time. The apartment was a 10 meters from a supermarket, so we saved on eating (expensive in Helsinki) by buying and cooking our own stuff, but it was also right in the heart of dozens of restaurants and bars - including one we tried where no-one could believe a tourist would find, it was supposed to be 'for locals' only. (so they were very friendly!). Free unlimited wifi.
20 minutes walk to the train station one way, and the port the other way, although buses and trams and plentiful (although at 2.50EU per ride, not super cheap). We enjoyed Helskinki, and I loved coming back to this little 'home' in the middle of it all both nights. I thought it was excellent value for money, and made a nice change from just another boring, faceless hotel room. I felt we got a taste of what it's like to really live in Helskinki by staying here.