The C5 has been described as "one of the great marketing bombs of postwar British industry"[3] and a "notorious ... example of failure".[4] Despite its commercial failure, the C5 went on to become a cult item for collectors. Thousands of unsold C5s were purchased by investors and sold for hugely inflated prices, as much as £6,000 compared to the original retail value of £399. Enthusiasts have established owners' clubs and some have modified their vehicles substantially, adding bigger wheels, jet engines, and high-powered electric motors to propel their C5s at speeds of up to 150 miles per hour (240 km/h).