How much weight will a French cleat support? Planning on attaching a 48" shelf. The cleat will be made from MDF, but accepting suggestions there. Will be attached to studs 16" on center. Any experience with metal Z clips as an option? There will be some corbels at each end to help keep shelf from tipping forward.
A French cleat does not add any additional strength, it will hold as much weight as the fasteners in each half will support. It is basically a convenient way to hang something such as a cabinet or framed mirror on a wall.