I go to Vienna at least 2x per year and I can say I've never heard of the place.  I took a glance at their website and it looks like a pretty standard Vienna Studio-type brothel, of which there are literally over a hundred of all different types and quality.  I found one uninspiring review from 2012 on brothelvienna.info just by searching on "Club 28".  There was nothing on the English language sex-vienna.com.  The German-language erotikforum.at has entries you can find using a search.  Once again, it appears to be very average.  There are a lot better alternatives for the same amount of money.