I see so many of these performance chips advertised on eBay - is this just snake oil, or the real deal?

I have heard RPI have a good product, but does anyone have experience of these eBay wonders? and given the fragile nature of RR electrics, would I be a real eejit to fit one?

The RPI one is fitted to my 3.9 RRC. You will need to blueprint your engine to get full benefit (or at least make sure timing chain, camshaft and tappets are new), and mine is the dual fuel one so gives an extra 10 degrees of ignition advance when running on LPG