The apartment has a nice, quiet location in Hel, and it would probably be great during the warm weather of high season. We stayed here during a cold weekend at the start of May, though, and we were a bit uncomfortable. The hosts brought us a space heater on our second day, which helped, but even then, and with a fire in the fire place, we were cold. I'm not sure I'd recommend staying here during the off-season.
If there weather were nice, I think this would be a nice flat for a family. There's a patio and a small garden in back that we couldn't really take advantage of, but which looked pleasant. The location is good, and it's only a short walk from the apartment to the primary attractions.
The amenities are generally okay. The kitchen is pretty nicely furnished, but while we were there, there was no hot water there (only in the bath), and that made washing dishes a bit of a chore. (There is a dishwasher, which we used, but even rinsing the dishes or wiping down the counters was a cold process.) We found the beds comfortable enough. Although there is a chest of drawers, there's no wardrobe or closet in which to hang clothes.
At the right time of year, I think this would be a nice apartment for a family vacation--but if the weather is cold, I might look for something else.