TDI PD Powerboxes for Sale on eBay

.......since I'm probably going to buy another 130hp TDI PD Ibiza, I wanted to ask what those small 'tuning boxes' are all about that are sold on eBay! In my Ibiza GT TDI (AFN), I had several cheap eBay power boxes in it (around 99 euros) and eventually a very good one from KW-Systems (with remote control) (599 euros)!
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'These small Powerbox devices are offered for €15-25, which seems incredibly cheap – they can't possibly be any good, right? Basically, all these boxes do the same thing: distort signals. But why are these PD Powerboxes so inexpensive?'
'They promise a power increase from 130 to 150 horsepower. However, my friend's Audi A4, which already has 96 kW, is putting out 151.4 horsepower on the dyno without any tuning... It's just ridiculous to make such claims! OBD-II tuning is a tricky thing; I wasn't happy with the tuning on my current Alfa JTD and would have preferred to get a power box from KW-Systems (with a remote control, of course)!'
Regards,
Monchi.

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...and also worth recommending:

/viewtopic.php?t=2855&postdays=0&postorder=asc&start=15 (read completely!)