They work well. I have a set on my car. 5K miles so far and no issues or leaks. I've had to remove the headers and re-used the inserts, and still no leaks. The aluminum frame is nice.
The graphite inserts are fragile as far as dings and dents go. I think they are just pressed graphite. If the flange flexes too much during installation the inserts can fall out. At least that is what I noticed on mine... But, they have sealed well for me so far.
I think the aluminium frame on mine is only 3/32 - 1/8 thick. Before I installed them I was moving them around and I think I picked it up by one end and a few inserts fell out. It was a error on my part. I'm not saying they're bad. These have worked better than anything else I've tried.