A fork mount is the most secure mount there is, and induces the least amount of stress on the bike, far less than attaching a wheel to the fork and riding it. At least the upright mounts these days clamp the front tire instead of the downtube, and they do serve a useful purpose for bikes that do not have a standard fork and quick release. Upright mounts were originally designed for consumers who thought it was too much trouble to remove a front wheel and did not know how to properly adjust a quick release skewer, thus creating a safety hazard. It was figured that the less the consumer messed around with bike, the better. And better to have them mess around with the more difficult and sloppy process of attaching a bike to an upright mount, than to suffer the loss of the front wheel while riding from an improperly adjusted quick release. The newer upright mounts are much improved and do have their benefits, but being more secure and/or causing less stress to a bike are not among them.