We loved our stay at Robert and Pavel's place. The location is fantastic, the apartment is gorgeous, and our hosts were incredibly responsive and communicative throughout. We also really enjoy the epic "our favorite spots in the neighborhood" booklet they put together for guests. We're quite familiar with Zizkov, and even we found a few awesome new places via their suggestions!
The only blemish to our stay concerned the building heating system which started making a dull buzzing sound at night, making it difficult to sleep without ear plugs. Robert and Pavel did a great job managing the situation and communicating with us throughout, though the issue wasn't yet resolved by the end of our stay, so consider giving them a ping to see if it's been resolved if you're looking to book in December 2018.
All in all, we can't recommend Robert and Pavel's place enough, and would absolutely come back again.