We used them, but in a roundabout way, since I first found one of their apartments on Air Bnb, which was unavailable (Stalin Terrace). They sent me a helpful email offering different apartments and we ended up booking the Mike and Franca suite, which we loved. It was extremely tiny but the (detached) terrace with outdoor shower, nice furnishings, and incredible view, made it worth the splurge (only apartment out of six that we exceeded our $200/day budget). It was located by the way, directly beneath Elizabetta recommended above, and they seemed cute too. Check in was at a tiny office on the main street of Vernazza, quick and impersonal, and we followed the agent up up up to the suite. Very clean, wifi worked. Bathroom was contemporary and regular sized, but the bedroom was so tiny we stored our luggage in the laundry closet we found on the terrace...which turned out to be a good thing, as there was a laundry sink and drying rack in there, so we did our laundry and hung it to dry in the crisp Mediterranean air!
The view was amazing, this unit looks directly down on the "second" beach in Vernazza, so the people watching was fun, and we could pack a bag and go down there for a swim in the morning or afternoon (when it wasn't packed). We even rented a small boat one day...