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From the photo this seemed to be a Chinese copy of the Hidersine Maesbury which I use and love, so I bought it for backup. Its price varies (disappointingly, from 8.99, what I paid, to 11.99 now), so shop around, or wait; or the Hidersine is about 20, so it won't break the bank. The Ammoon has slightly less rubber padding and is not exactly the same length, but bout sizes vary anyway, and it has one more screw hole than the Hidersine, so more adjustment is possible. As I say in the Maesbury review, the rubber in contact with the shoulder doesn't have a lot of friction, and this kind of anti-slip matting glued on perfects it: - https://www.amazon.co.uk/gp/product/B00AVJ9GBY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1