Yeah, that city compost sounds like the stuff we get here. Really chonky(chunky), big pieces of wood chips and such...steaming hot.
And they seem to give you the same amount every time, whether you're just driving a pickup truck, or have a 6' x 12' utility trailer...hope your suspension can handle it.
But I tried to use that for a few gardens years ago, nothing really did well for a coule of years. After that it was great. But I don't think it would be too good as a potting mix. Maybe if you let it sit for a while and let it finish breaking down. Or sift the big chunks out, but that would be a whole lotta work.
But anyway, what he said, top dressing...I only use it as mulch now.