re: GIK acoustics in the UK
a friend just bought some and the quality was distinctly suspect. Some were half filled - some were damaged. Support was basically useless.
Their answer to the half empty corner trap was “talk into it and if sounds muffled then it’s fine” (!) - I’m hoping they sort it as I suggested he buy them but not looking positive so far.
FWIW I normally build them myself using rockwool RW3 - you can make custom sizes and it’s 10% of the price of buying them.