The hosts were very speedy with their replies and accommodating with changes (initially booked for 4 people but increased to 5 without any issue).
The apartment itself is an absolute bargain for Vienna - not particularly big and about a half an hour walk (or train) to the city centre but it's to be expected for the price.
Only real complaints were the WiFi not working and having only one set of keys but neither really mattered. Would recommend for those wishing to stay!