One way is reversible, the other quite permanently ruins your paint.. If you get the fake stuff wrong, you can reheat it and try again...ruin the real stuff and you're out big coin...
Not everyone is up to the task of laying real CF and if the tolerances are tight, the extra thickness can mean stuff fitting or not...
Glad it worked for you tjoz, but there is nothing inherently wrong with the 3M stuff, except it's an effect, not real CF.
Personally, I think it looks good on interior small trim items, but wrapping a whole roof or bonnet, looks crap...
If you're going to add even more weight to your car, make it stereo components. CF and resin over steel, joke.