Having raced with the Success Ti rear derailleur for a couple of years in the early 80's, I thought it was well designed and constructed, and shifted very well and reliably (for the day). It was Huret's high end derailleur at the time. The thing about it I didn't especially care for was the plastic cap that fit over the mounting bolt, as it was prone to getting lost or broken. OTOH, the Success Ti rear derailleur had two cage mounting holes, so one could optimize the cage location for close ratio (corncob) freewheels or wider spaced freewheels up to 28t. This was a nice feature. I still have a nice example of the derailleur (with plastic cap) in my stash.
Kevin Ko
Eugene, OR