I have used these combs several times. They are very flat. I sew them down with weave thread NOT SEWING thread. I use these in my U part wig and since the price is so cheap I just order say 6 small and 3 large so I have enough for the future. I don't order just 3 cause then what you gonna do with your next wig? These combs are super flat, my hair is short in the front and it layed so flat, I really did not need any type of bonded track. Also the combs do not break, they last longer than my U part. I would buy them again.
Also, I have never been able to find these flat wig combs in any local beauty supply, this appears to be a online item only.
I use invisible thread anytime with my lace wig its thinner and just as durable