I agree the Benro GH2 is a fantastic gimbal for the money compared to some of the high end ones at nearLy twice the price. It worked fine with my 600mm Canon f4 mounted when I had it but the Sigma is a lot lighter lens so I'm sure the Beike at £55 would be okay as I used that before I got the Benro with no problems at all.
It's really down to your available cash, the Lensmaster falls somewhere between the other 2 for price and is well regarded and used widely these days.
Don't be put off too much by the low price of the Beike though as its a decent head imo.