I can also confirm that it works great with flat surfaces.
Clamped a couple of times to bars/counters, tables, poles, lighting rails, stage lip (of var. dimensions) and never had a problem.
I'd only worry if a surface (like a bar/counter) was **not** perfectly flat but cone-shaped. But, in such a situation,, some wedges won't help you, either.
Make sure to get a Manfrotto swivel adapter (or equivalent), too - unless you already own one.