The photos don't do this place justice - the room is HUGE. We did worry that we'd not actually picked somewhere with air conditioning, but there are two large fans (not too noisy so as to affect sleep) which is absolutely fine when combined with a ridiculously large room and nice marble floors. You'll occasionally hear the gondolas/tourists down the little canal alleyway, but the shutters on the windows are very effective.
The location is extremely good: you are genuinely only a few minutes from San Marco, which is particularly useful when you've got yourself lost in the city again - you just have to navigate back to San Marco and then find this place again. Literally outside your door is a square with some restaurants, a pharmacy and some other bits. There was an initial worry when we first got in as the entrance is down a tiny alleyway, but it turns out that everywhere in the city is down a small alleyway and this is in a very public place, so not to worry about it.
Nikos himself may or may not be on hand, but he always made sure that we knew who to go to if there were issues and when we needed to do key collection/drop off: he was based very nearby (maybe 2 minutes walk away) and generally very helpful and friendly.
Highly recommend!