I have the strong strut. To be completely honest....you'll probably be fine with any of them as the E39 Chassis is quite rigid on it's own. The rogue bar is another that I'd certainly get if I had to replace the SS. Mason also makes a quality product, but not sure if they make them for the E39.
theyre design is ever so slightly different, if u look at that extra reinforcement that connects to the mounts from the bar. i believe it helps with access, to the 3 nuts but also reinforces the weak area on the strut mount