Modern Vespa

I'm looking at buying a 2021 Piaggio Liberty 150. Can anyone tell me how comfortable this scooter is for a passenger. I need to get a luggage box with backrest included I know that will help but in general how is the scooter for a passenger.

Can't speak to this model, but it might help to know the size of the rider/passenger and distance intended....

A used low mile Honda SH will pull 2 people way better than a liberty 150. SH =15.5 HP. Liberty = 12 HP. And they are way easier to work on. The Honda has a coolant drain plug in the water pump housing and a bleed plug in the thermostat housing. I can do a coolant swap on my Honda in less than 15 min. Piaggio and Vespa don't understand the concept of easy to understand(and false information)service manuals.
And the best part is, it'll cost half as much even if you have to replace the tires and swap the coolant.

I ride my wife on the back of our Liberty all the time. I have a 37 liter Kappa trunk on the back with the back rest pad. She likes the ergonomics just fine and we've done up to 60 miles one way. She's comfortable as passenger on the seat, but I have to slid forward and sit slightly the nose of the seat. We're not fat per say, around 200 pounds each, but I think a little longer seat would have been better for me. But then again we got the Liberty for bunpin' around on, and it works great for that. Running errands and commuting to work. The Liberty does fine with a passenger but I installed the lighter AF1 rollers for better take off. For any ride further/longer we have a Honda Silverwing.