I've been a long time customer of Bitmain Comp. (4+ years) and have recommended them as the best supplier of mining equipment many a time. Service is spotless, prices are competitive and deliveries swift. I've recently purchased a few components I couldn't yet put to use, but I have complete peace of mind that if anything was wrong then they would sort it out very quickly. As expected it all arrived next day and I've now confirmed everything works as intended.