I have a substantial amount of GIK panels (absorption and diffusion) in my multi-purpose listening room/home theater. Half of my 16x29 room is for 2 channel listening and the rear half of the room is a home theater system. I have a total of 13 absorption panels (from 7" Monster bass traps to 4" full range absorption panels) and 8 diffusion panels which are all in the 2 channel listening side of the room. To some degree it is overkill on the Impression diffusion panels because I was working on a visual centerpiece for the system with the panels. But the combination balances out.
My experience with GIK over the past couple of years has been they may be the best value source around for quality panels, clearly they have built a large platform for themselves with their customer service, training videos and discussion communities. I cannot fault them in any of these areas. They have a huge variety of products with a lot of customization, premium fabrics, and art panels, etc. The build quality has traditionally been solid if a little basic. Most importantly I have experienced excellent results both from working with their advisors and the actual panels in my room.
For the not-so-great, I think they have experienced severe growing pains since COVID and have had order fulfillment times extending 2-3 months. This was last summer when I ordered, in the fall when I ordered, and in December when I ordered again, each time at least 8-10 weeks for fulfillment. Comparing this to 2019 when I ordered and got my panels in 2-3 weeks. Chalk this up to all the people staying at home for the past year and deciding they want to experiment with acoustic panels. I think also their QC has suffered just a bit during the COVID crunch. My recent orders have had lots of splinters, some of the fabric is creased and wrinkled on the front of the panels, etc. Compared to the panels I bought in 2019 I experienced nothing like that.
I'm sure they will get back on track once things settle down from COVID - I don't know what kind of workplace issues they have run into but obviously demand and shortage of labor has been an issue for them. Just some things to consider if you're planning on ordering anytime soon.