I had a great stay at John and Katrin's place. It's a nice place to feel at home for a few days :) I didn't meet the hosts in person but they were very friendly and responsive with any requests.
Just two things you should know: As a light sleeper I was sometimes woken up by a weird noise the shower makes. And at the time of my stay they didn't have a fitting key to lock the room. Since it's not that many people staying in the house I don't feel like it's a big deal, but maybe ask them in advance if that's important to you.
The WiFi connection is speedy and reliable. You can get pretty much anywhere in the inner city within 35 minutes. Overall I'd really recommend you stay here, what John and Katrin have on offer is hard to beat at this price point!