Does thermage and liposuction really work on flab?

Yes. Thermage can tighten skin to a variable degree. Liposuction can remove fat beneath the skin and cause a little tightening as well.
Different targets. Thermage is a radiofrequency device that, by heating the protein in the dermis (collagen), there results a shrinkage of the dermis thereby tightening the skin. Gradual new collagen is also stimulated in the upper dermis, laid down parallel the skin surface. Helpful to some degree in fine skin wrinkles and skin excess. Liposuction removes unwanted subdermal fat, permitting redraping of skin.
No and Yes. Thermage may reduce nominal amounts of fat whereas liposuciton definitively removes localized fatty deposits.
Depends. Whether either of these procedures will work on “flab”, depends on patient physical examination. Neither one of the procedures will do well for patients who have poor quality overlying skin elasticity. Each procedure has very specific limitations as to what can be accomplished and which patient is actually a good candidate….