We are in the beginning stages, but so far the experience has been very positive.
Within hours of leaving a message notifying them of our selection, they contacted the donor and then reported back that she agreed to cycle with us. I'm sure it doesn't always move this fast, but within one week of receiving our deposit and fee agreement, the donor scheduled and completed her psych eval and we received the contract to review by e-mail.
I think they have more available donors than are shown on the internet. The profiles are pretty extensive and include multiple photos of the donor, ususally at various ages and some include family photos as well. The photos on the website don't necessarily do the donors justice. Viewing the profiles in their office gives you a much better idea of what the donor looks like.
They keep the site updated, too. Within a day or two of our verbal notification we wanted our donor (and not the receipt of money, although it was in the mail), they updated the site and her profile was removed from the available donors. Another donor we were considering was booked by another couple and the site was updated quickly to reflect that.
The donor compensation is a set price, too, so you know what that is upfront and don't have to worry about sudden and mysterious changes in the amount.
Anyway, so far, so good. Very professional and friendly to both IPs and donors.