I've been toying with this below from BSR, member WIDE in Sweden has one and reports good things. You get the unit to remap yourself so can return to stock as and when. And its £499 in UK with he PPC unit as I spoke to their UK dealer. Figures are about 300bhp.
https://en.bsr.se/tuning-kits/t/2784/volkswagen-golf-vii-20-gti-230hp-2013-2018-chha-cnha
Why would anyone based in UK look for tuning options in Sweden is beyond me, especially for those prices.
Apart from the big name branches, tuners here are either expensive, not knowledgeable or a combination of both. At best they offer average, off-the-shelf tunes at expensive prices, falsely advertised as "custom" tuning. So many trusted options in the UK if you do some investigation in MK7 tuning forums and groups.
You like you warranty? Get a JB4 that has the best and safest results in tuning boxes.
You want to get every last bit of performance or close? Custom tune it in the UK.
This BSR kit has nothing to offer to you. After the first ECU flash (which is what it does) your warranty is gone anyway should you ever (knock wood) need it. Flashing back to stock in these cars removes the flash traces as much as driving in reverse reduces the car's mileage. If it's simply reverting to stock for selling up most tuners would do this for free I believe.