Both systems have the same stability, as they generally use the same mounting points. If using the Wingrack side-frames to mount just sidecases with no top case we will suggest that a bridging kit is installed in order to generate extra stability. The hardware is designed to be a permanent attachment, but it can be removed relatively easily if you want to. Yes, with the majority of bikes you can add a topcase at a later date. The cases are made of a durable plastic Polypropylene.
Acrylic paint is used for the gloss finish cases.
If you purchase the largest cases you will be adding over a foot to each side of the bike. Also consider that the hardware itself will be mounted approximately inch from the rear bodywork. GIVI replacement shields are generally 2 to 4 inches taller than regular stock shields thus generating a wind deflection of an extra 6 to 8 inches over the stock shield. The majority of the universal shields are also light-smoke tint, but the Cruiser style shields are available in clear only.