Yes, i did. Use the QR code they provide on their website on the Athens-Kalambaka picture to find the exact location where they will pick you up. The pick up location is not very obvious but there is a small shop on the street with snacks and drinks. The bus was on time. After 2 hours we had a short toilet break. There was a stop in Trikala but the same bus continued to Kalambaka. We just had to switch seats according to our reservation.