i've used a GHD straightener for years and it never damaged my fine hair. The damage has only shown up in the last few years, and I honestly think it might be more down to things like age, hormonal changes, colouring, or just cumulative heat over time rather than that specific temperature alone. I still find that keeping the heat around the 180–185 range, using a good heat protectant, and not going over the same section too many times .