We had a great time on this tour. Because it was private, we could choose where we visted and whether or not we went into the Palaces. We decided to go into the Quinta da Regaleira and I 10/10 recommend you do the same. It's so unique and the grounds are huge - you could easily spend a full day in there. We also visited the National Palace, Pena Palace, and Europe's Western Most Point.
Our tour guide, Francisco, was amazing. He's super knowledgeable and kind and really catered the day to us. He was at our Airbnb pick up location early and was a very safe driver. He did a great job of balancing guiding us around with giving us space. For example, he was with us for about 30 minutes in Quinta da Regaleira and then let us explore on our own for 45 minutes.
We've done guided tours before where you're on a giant bus and getting herded like cattle - this was such a good relief from those. It felt like we had control over the day and how we spent our time, with lots of great advice and guidance from Francisco.
The food was great. First, we stopped at a pastry shop in Sintra and tried two local pastries (not pastel de nata, since you're likely to have that 12 times on your trip to Lisbon) and espresso. Then for lunch we went to a seaside restaurant with incredible views of the ocean and great food.
One thing to note is that tickets into the palaces and food is not included in the ticket price. This listing says that very clearly, but it's worth repeating. The pastries were cheap - about 6 euro total for 2 pastries and 3 espressos. Lunch was pricier - about 45 euros. You can look up ticket prices for the palaces you're hoping to enter. Everywhere took card or cash.