I've only been in mail correspondence with Bernhard, but even so he has been very helpful! I couldn't come to think of anything to ask that he hadn't already thought of.
The apartment is wonderful and located in a superb area in walking distance to the city center and with marvelous restaurants and easy opportunities of transportation in the neighborhood. It is bright, friendly, modern and very tidy and clean. The roof terrace is splendid for breakfast in the morning and a cool glass of white wine in the evening. Only note - and this is a VERY small one - is the lack of a parasol and some darker drapes of some sort to keep the morning sun out (which would probably spoil the airy feeling of the apartment). So remember your sleep mask :)
I would definitely rent the apartment again if I was to ever come back to lovely Vienna!
Enjoy!
/Anne.