I had SJD and muscle separation and wore tubigrip, as well as a couple of different bands with velcro that i bought. It did help. It actually made me feel better the instant i put it on. I don't know if it helps reduce tummy size? It helped me feel better, and it enabled me to be more active. Possibly these things help reduce tummy size?

Tubi grip was cheap ($20) from the physio. The other band i had was an Oppi band and i can't remember the other one.