I don't see many Victa Vacs around so probably a little rare ,may be harder to sell than a standard Victa motor as it will fit less equipment ,could be less sought after.
Mini Bikes and Go Karts can use a 3/4 centrifugal clutch but with the standard engine they use a clutch adapter so using this motor on a Kart would save buying the adapter but without the threaded crank end it may make things more difficult.