I appreciate everyone's feedback but I am still curious if there are any professional PM's with case studies. For example, let's say you manage 100 properties and over the last couple of years some have decided they no longer want to list on VRBO. Did the occupancy rates of those properties decrease in a way that similar properties in the portfolio did not decrease? I know for certain there are professional PM's that stopped listing on VRBO a few years back when they changed their policies, but I don't know those PM's well enough to get the relevant data.
My first inclination was "I need 5% or more increase in occupancy to make it worthwhile". So I went on the Google machine and according to AirDNA you get a 4% bump by being on both. Falls a little short of my 5% but it is close enough to make me wonder. My high value nights are going to book with or without VRBO so really that 4% increase is going to come from the lower value nights. So the increase in revenue probably ends up being 5-6%.
Maybe I am over estimating the cost though. Maybe I don't need 5% to make it worthwhile? Can you really manage both platforms without paid property management software? You have to keep the calendars sync'd, the pricing sync'd, the photos sync'd, the descriptions sync'd, guidebooks, messages, etc, etc.