[Al Skierkiewicz]

aldaeron,
I just want you to be sure as I was a little confused when I first looked at your post. The angle aluminum shown in the bumper drawing is to secure the cloth covering to the plywood backing. It is not the attachment but is merely clamping the cloth in place. In the drawing, the bolt threaded into the blind nut is the attachment.
The drawings you submitted are both used by teams but the one using the additional angle is sometimes more easy to remove. However, the support angle is generally weighed as part of the robot.
From <R07>

G. Each set of BUMPERS (including any fasteners and/or structures that attach them to the ROBOT) must weigh no more than 20 pounds.
H. BUMPERS must be designed for quick and easy installation and removal, to aid in weighing and inspection (as a guideline, BUMPERS should be removable by one person in less than ten minutes).
I. BUMPERS must attach to the FRAME PERIMETER of the ROBOT with a rigid fastening system to form a tight, robust connection to the main structure/frame (e.g. not attached with Velcro). The attachment system must be designed to withstand vigorous game play – nut and bolt fasteners are recommended. All removable fasteners (e.g. bolts, locking pins, pip-pins, etc.) will be considered part of the BUMPERS.
J. If a multi-part attachment system is utilized (e.g. interlocking brackets on the ROBOT and the BUMPER), then the elements permanently attached to the ROBOT will be considered part of the ROBOT, and the elements attached to the BUMPERS will be considered part of the BUMPER. Each element must satisfy all applicable rules for the relevant system.