I think their popularity varies by region/state. Here in Oklahoma, you see very few Dums/MGBs/MTBs for sale at shows. I can count on one hand how many MGBs/MTBs I have seen at shows in this state in the last 10yrs.

Even Dums are still not that common around here.
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Pat Higdon - Higdons Herps, Tuttle, Oklahoma USA
Oklahoma City Herpetological Society Member
4 dumerils boas, 2 rosy boas, 3 burmese pythons, 1 reticulated python, 1 ball pythons, 3 borneo pythons, 10 bearded dragons, 9 leopard geckos, 4 african fat-tail geckos & 1 sulcata tortoise