We spent two nights with our 2 year old. The appartment is functional, very clean and has everything you need. Its indeed very well located with just a 3 min walk to city center and 5 min to the lake.
In summer it's very warm under the roof which is why you probably would rather want to spend time at the beach, in the mountains or in the city instead of hanging out in the flat.
communication with Sebastian was very good, check in went smoothly.