Its legit... by chinese laws, bitmain can not sell this machine in the mainland by any cryptocurrency, they sell it only in RMB... you can check their chinese website
https://shop.bitmain.com/main.htm?lang=zh

and also by chinese law they must tell how many machines were available for sale... and in their announcement by Wechat account, they state there was 6000 machines just for mainland china

开售产品
蚂蚁矿机 A3 815G （适用于Blake2b算法币种）
功耗：1275W+7%
暂定价格：20800 RMB
开售时间：1月17日下午2点
本批数量：6000 台
发货时间：确认付款后7个工作日左右发货
备注：
1.现货产品无法修改地址
2.本批机器每个账户限购一台，不能使用优惠券
3.订单付款后需在官网上传付款信息，并把“订单号+付款人+付款金额+付款凭证”发给微信客服
4.付款需在2017年1月17日下午4点到账，逾期未到账订单将被取消

BTW, im not chinese... just been teaching english here for a few years