I fitted one to my last 8v and I'm sure it came from the seller in your first link.
The chip arrived with some decent colour fitting instructions, I had it fitted and the car up and running again within 30mins. I wouldn't say it made a vast amount of difference, maybe a little bit smoother in the mid range, I did feel happier with the way the car drove afterwards though.
I think you will only notice any major change if you were running different cams, an induction kit and a different pipe.
I still think for the price they are on ebay they are worth trying like I did.
Tobz