Good thing about blood sugar problems is that they're objective. Unless you've got a defective glucose meter, it doesn't lie. Either your sugar is positively affected by something you're taking, or it isn't. Placebo effect shouldn't enter into it unless you're just going on the way you feel as your blood sugar barometer. Blood sugar is the only thing I don't recommend going on the way you feel as a way to gage, at least whether or not it's high. YMMV. Low blood sugar is a bit easier to gage on symptoms, though. Are you high or low?
Anyway, chromium never made a noticeable difference in my blood sugar (I'm hyperglycemic) or the way I feel. I take GTF on faith, because we need chromium. I experimented with different dosages for a while before deciding it didn't do anything for me, though.
Resistant starch, probiotics, and a whole foods diet without added omega-6 fat is the only thing that's ever made a lasting beneficial difference in my blood sugar. I actually have hope I'll be normal by this time next year. But it's a long haul process. If you're low blood sugar you might be a little different, although I think some low blood sugar people like
@Sidereal have had good results with gut therapy, too.