I bought a Sigma 18-200mm from them, very happy with the purchase.
The lens developed a fault and went back to Sigma through Microglobe. Not very happy with MG's customer service - 'certainly sir, I'll call you back tomorrow with an update' and no phone call. I was promised updates at least four times and they NEVER called me back. I gave up in the end, and had almost forgotten about the lens when it was delivered about two months after being sent in. No cost to me for the repair though, I just got the impression they were more interested in selling than supporting a product.