Vampliers is a well-known brand, made in Japan I think, so I think it’s more likely a partnership or competition than a cheap knock-off.
Engineer brand products are mixed where Vamplier is more focused on tools so the later may actually be the original manufacturer with the former the distributor. In Asia, this sort of arrangement is pretty common when manufacturer lacks resources to address oversea-markets.
SS-02’s are always cheaper on adafruit. Even with prime.