Hi Martin, we have booked online for years (Turkey ) would not do it any other way, never had a problem.
Looks authentic site, nice place, we are planning on Dalyan as well, Merhap same area as Dede, when are you going we are off 18 th June.
I don't think you have anything to worry about, I am sure you will have a good response from every one else who books the same way.
I find its much more straight forward, you get picked up in a nice AC mini bus, avoiding all the hassle waiting for everyone else and wizzed straight to hotel, the owners get a bit more money than they would via a company, so you are treated more like royalty than usual, once you have tried it you will never go back, enjoy Joan