Should I take a chromium supplement?

The short answer is "no". I'll quote the ADA's longer answer, from the May
1994 _Diabetes Forecast_, p.73. The ADA's editorial board says:

    Some popular books on diabetes have claimed that chromium, which is
    found in many common foods such as animal meats, grains, and
    brewer's yeast, is good for people with diabetes. Not so. Though
    chromium supplements may benefit people who are significantly
    malnourished and have an actual chromium deficiency, there is no
    significant evidence that consuming extra chromium helps people
    with diabetes who are even close to being well nourished.

    Taken at the dosages listed on the bottle, however, chromium is not
    likely to be harmful. But your money is better spent on more useful
    items!