Rebound XT by Designer Supplements and Gaspari’s Novedex XT apparently both contain the same substance, a steroidal aromatase inhibitor related to Exemestane. It seems to work better, or at least provide a better bang for the buck, than 6-oxo.
Reducing estrogen will cause testosterone to increase. Reducing estrogen too low for very long is unhealthy. I’d only use something like this short-term, and then only if there is a good reason to temporarily lower estrogen.
I took a bottle of Rebound several months ago. Started at 3 caps/day for awhile, then 2, then 1 (tapered down to avoid estrogen rebound). It seemed to help reduce the size of some small lumps of gynecomastia I have.
I wouldn’t take any AI for long periods unless I had a problem with excessive estrogen and was having levels tested periodically.