They are both good products, and both very different. In fact I see nothing wrong with using them at the same time.
Targex is site specific and DermaTherm is not... so you could apply the targex to the specific places you wanted toned and then the DermaTherm to the rest of the body.
Targex reduces Cortisol where applied, hence why it can reduce fat, but wont you gain the fat back once you stop, and Cortisol is being produced again?