I haven't used it over Poly, myself, but I doubt it would give you much better sheen without a LOT of work, time, and patience and multiple thin coats rubbed in and wiped off, then polished. I do know you will need to lightly burnish between cured coats #0000 steel wool or similar (I use 600 grit sandpaper instead) I do not have the patience to wait several weeks between coats for cure time, so at best my use of T&T Original (or varnish for that matter) mostly results in a matte finish - although in some denser woods, and a few bowls I have recoated several times, I can get close to a satin sheen after 2-3 coats.
Nice thing about Tried & True, if the item hasn't sold before I get around to it (or if it has sat long enough that I decided to add a coat) a new coat can be added most any time, and it'd build up over time. If I wanted a shiny surface, I'd just go over the poly with some 400 grit paper (lightly, just enough to scuff it a bit all over) and re-coat with wipe-on poly - which will dry faster and give quicker results. (I use Miniwax Fast dry poly in Warm Gloss)
Given that it is a bowl, and already coated with Poly, I'd just use more poly , rather than try to work up a T&T finish - Generally I finish most of my bowls that may end up as "utility" with straight-up Tried & True and just go for the 1 or 2 coats and an extra rub-down after a few months if it hasn't already sold - a few I have added another coat or two over time, (which are the ones I got the satin sheen to them).