I haven't looked into TG100 specifically, but I've been taking (a) Now Foods liver powder, (b) Standard Process Symplex M, (c) Standard Process Hypothalamus PMG, (d) Natural Sources Raw Thyroid Glandular, (e) Natural Sources Raw Multiple Glandular, and (f) Allergy Research Group ImmoPlex Glandular.
I think there's something to the adage that like nourishes like. I figure the hypothalamus supplement may help with leptin sensitivity, the thyroid supplement may help boost metabolism, Symplex M may help with production of growth hormone and testosterone, and the multiple glandulars may just kind of help with everything in general.
They're all fairly cheap, so it's worth a shot. (And the doses are all really small compared to eating the actual glands, so I doubt there's any danger of adverse effects.)
This podcast on the subject is worth listening to.