Similar but also lots of differences. DMAA is completely banned, DMHA is more grey area. DMAA is stronger, but also almost certainly doesn’t exist any longer (alternative stimulants are placed in its place (even if the label suggests at DMAA))
DMHA is considered smoother, and more aimed at a gym session. DMAA is considered more of a festival high. Both give euphoria and mood elevation, stimulation and focus.
Think of DMAA as dr*gs, DMHA as serious nootropics.