I used to use the Bigmos handheld for about 8 months. Up to about 400mm, it was good. At 500mm half the time the OS didn't seem to work perfectly. Then I (and Sigma) figured out that it does work properly, it's just that sometimes the amplitude of my arm shake at 500mm is more than what the OS is able to overcome 
Anyway, I tested my Bigmos on a makeshift monopod (my tripod with the legs unfolded), and it worked like a charm. So I invested in a cheap but decent monopod, a Manfrotto 7.. something (the "Digi" model), forgot it's model number, and a 234RC head. It was about 65 bucks. Light and relatively stable. Makes my Bigmos a lot more stable, I can recommend it to anyone looking for an inexpensive but decent monopod.
By the way, here are some pictures from the last couple days. Cropped and PP'd as usual, except for the first, that's just resized.














