I fitted chips to my previous GEMS RR, at vast cost. Yes the engine did run differently, it was just perceptable. Did it increase power/torque in a way I could feel? Not really. Was it worth the cost of £750? Not really. I chipped my Disco TD5 and Freelander TD4. They cost £150 to £200 ish each. Could I tell the difference? By hell I could! So, chip a standard petrol engine with no turbo - nope. A tuned petrol engine is a different matter, my Lotus SE Turbo was stock 167 bhp, after modifying and chipping it's at 230 ish. So overall, no, I wouldn't chip my Thor 4.6. Not unless it was only going to cost £150 ish, and then just for the fun of it.
The claims of better economy - they sort of say that as the engine is producing more power you'll use less throttle to acheive the same acceleration/speed over the same road as when pre-chipped. Hmm. In any case, you've got a 2 ton car with a 4.6 V8. You can't really go about asking for economy now, can you? You have LPG anyway, so you're running at half the cost of mine.