I have not been to that specific hotel, but have been to two other kinderhotels in Austria. Our experience has been excellent and we would go again in a heartbeat.
As to the english speaking issue, we have found both times that the staff speak a good level of english. In fact, my husband wanted to practise his german last time and was frustrated as they kept answering him in English.
However, we also found that in the kids club, although the staff COULD speak English, whether or not they did depended on how busy the hotel was. The first time we went, it was off off season (end of september) and our children we among only a small handful of children there. Most of the others were toddlers. So my kids were spoken to in English all the time.
The last time we went, we hadn't realised it was a German school holiday week. The hotel was packed as was the kids club (which had a lot of advantages in terms of the activities on offer). So the children tended to be addressed as a group when giving insructions etc and this was always in German.
My kids loved the holiday anyway and we don't as a family use the kids club for more than an hour here or there so it was not a problem for us.
Our waitress spoke good english the last time, but the time before it was not so good. Both times we got menus in English though.
HTH