I tried transmogging BC quest rewards using this on my lvl 20 and that didn't work.
You'll see them as available options when mogging, you'll hear the transmog sounds, but the gold isn't subtracted and the mog isn't applied.
Tried it out on a F2P account, you can only mog into stuff you have, so I could unfortunately not touch stuff I only had on other characters like tiersets or WOTLK quest items. etc.
theory: a lvl 50 char could probably mog into T2 if they're boosted through MC BWL.
hahaha opened two boxes on three different f2ps at the same time from the same invasion and all of them got a 35ilvl item.
5.57 server time, maybe there is something with the RNG/time?