My friend and I stayed at Ui Bai Valley for 5 days, and it was great. The lady, Aphorn, who has the place is very sweet and helpful, a nice host. The guesthouse is about 7 kilometers away from the city center, it is therefore (very) necessary to rent a scooter, to get back and forth. Aphorn helped us with the renting, which was 200B per day.
The room was clean and comfortable, and had everything you need. We would definitely recommend this place, if you’re paying Nan a visit.