If you use just bunks, you only need 2 support cross members, as soon as you go to keel rollers you need more cross members. more rollers and all their accouterments. All this adds up to extra dollars on the cost of the trailer. You know how much it cost to replace the keel rollers, and just the support for the bunk rollers. Could easily add $1000 or more to the trailer cost. The boat manufacturer will sometimes include a trailer as part of a package. Often the new style "float on". Cheapest to manufacture. Mr Woods trailer is much better suited to launching and retrieving more then just a few times a year. The effort to crank it on is minimal compared to one with just bunks. Properly adjusted the weight is supported by the keel rollers the bunk rollers are just for alignment, and will support minimal weight