diesel tuning boxes?!?

anyone had any experience? i know this is a renault forum, but there are some clever clogs on here ;)

my dad has a meriva 1.7 cdti, had a quick google but there seems to be loads on there, just wandering if anyone has any experience of a good balance of improvements compared to costs, eg. dont wanna spend £270 really if there is one that costs half and does something similar.

my google results showed the dtuk one made good power, but no diff to ecomony, would rather have economy than power as its for my old chap