Andy
I'm in a similar position to you.
I've narrowed it down to
Chipexpress,
DTUK and I particularly like the sound of the
Spider box
I can't find much in the way of real life testimonials though.
I have spoken to a guy I know who does, amongst other things, ECU tuning. He is by no means a specialist but is pretty insistent that these boxes will not produce the effects they suggest and more over could cause problems with the Diesel Particle Filter because of the excess fuelling.
Sorry I can't add anything helpful but if you find out any more, please share.
Thanks.