Have you checked Italianspeed? My father and brother uses these for their Audi A3 and VW Passat and are very satisfied. I will buy one of those if I feel the need for speed in the future.been looking for some time at the below
https://www.racechip.co.uk/shop/peugeot/308-from-2007/2-0-bluehdi-150-1997ccm-150hp-110kw-370nm.html
And these
https://www.diesel-performance.co.uk/vehicle-peugeot_308_2.0-hdi-bluehdi-150ps
although to be honest I cannot understand the prices, and I guess thats the reason I have not picked one yet.
on my older cars Ive always used re mapping to the ECU like super chips however they leave a tag on the file which if looking for the dealers can see although its doesn't say whats happened but they would use that if you needed a warranty job doing.