Hi, Canucks,
I helped a friend when she planned her camino last fall. She didn't want to stay in albergues and wanted to have things all set up. She had considered several companies probably similar to the one you mention and showed them to me. When I saw the price, I nearly flipped and told her we could do it ourselves for 1/5 the price. And we did. It's easy to make reservations, many places have email, and phone calls can be very cheap (I have a plan in the US with 3 cents a minute calls to spain land lines, which is cheaper that what it costs me to call within Spain when I'm walking with my Spanish mobile phone!). It wasn't hard to do. As kiwinomad says, though, it really ties you down and I personally wouldn't want to have so little flexibility.
A happy medium might be to have a good guide book and just call a day or two in advance from the Camino once you're walking. Though I usually stay in albergues, I often take a break and stay in private places and I've never had a problem finding good options a day or so in advance. No matter how well laid your plans, I think most people find that they just can't predict how every day will go and are happy to have the ability to speed up, slow down, or take a day off. Buen camino, Laurie