I have a twin MB and love it for walking but hate it for shopping. I have hung on to my single and sometimes I use that and Tom walks or I put Tom in the single and carry James. Other times they both go in the double.
I tried a friends P&T and didnt like the maneuverability of it compared to my MB. Even with 2 kids in it I can steer it with one hand whilst texting
I also didnt like the storm covers on the P&T but the MB double ones are the same concept...no zip opening either (so I have been told...I just have a generic one now).
One PIA about the double MB is getting it in and out of the car...it is heavy and it is awkward. I have a 4WD and I kind of lift it and shove it.
in summary...for walking you cant beat the MB (IMO) but it has some downsides for other things like shopping etc. I tend to leave the single in the car and the double in the garage. We use the double if we are walking to things and the single if we are driving to toddler activities where James may need to sleep while Tom plays.
I am just starting to wonder about the kiddy board now as Tom likes walking.