I stayed in Mondello for 5 nights and all in all I had a very good time!
There have been a few problems in the first place but I told Pietro about them and he reacted very fast and came up with solutions for all of them.
The apartment's location is quite good because it's only a 10 minute walk to the beach and also to restaurants. There is also a big supermarket pretty close as well as a gorgeous bakery, which was rightly recommended by Pietro. If you'd like to go to Piazza Mondello or Riserva naturale Gapo Gallo this will take you some time by foot but it's still at walking distance.
The accommodation itself is equipped with everything you could possibly need and the style is pretty nice as well - I absolutely loved the loft-like construction with the bed on a platform. Of course you could see that the apartment is used on a regular basis and equipment like pots or pans might be replaced in the near future but it was all functional and I didn't bother about a missing handle or suchlike. The bathroom is quite big with a nice shower and you can also find a washing machine in the accommodation. It also has got a very nice front porch with outdoor furniture (plus a very cute cat that often visits in the afternoon).
Pietro is a fantastic host, who answeres very quickly, cares about his guests and tries to solve all possible upcoming problems and who is also very friendly and kind. Furthermore he offers an (very recommendable) airport transport service! All in all I had a good time in Mondello, thanks Pietro!