Dave Robinson does have great last minute deals, but they are not guaranteed. They only offer them if there is a unit that hasn't sold. And they are often very last minute, like a few weeks prior. So if you are banking on getting one of these deals, you may find yourself without a room.
He also only rents Sat-Sat (which are usually inexpensive days to fly) so there isn't a lot of flexibiility. If someone else books the condo you want, you have to change your plans by a whole week to get it. He rents this way so that there are never any leftover days.
Not booking is a real crap-shoot, because it isn't like a big hotel with tons of rooms. I would go ahead and book now, especially since you already have your flights because once the condo is gone, it's gone.
(BTW, we rented with him and stayed in 304 last November and LOVED it. I doubt I will ever stay anywhere else!)