They only have the posting key so I'm not sure what they could be doing with my assets that I wouldn't be OK with. I can see what they are renting for.
Yes I used to use Peak and I agree 20% seems a bit steep in comparison but it is a huge time saver for me. It's difficult to measure the exact increase in DEC because of all the recent changes but it looks substantial to me, even with the 20% fee.
Apart from the time saving aspect the biggest advantage seems to be that the cards are rented for a higher percentage of time at optimum rents.