The BEST/SAFEST hair fibre there is (Uk accessible)

[Ht2]

As long as the hair fibres are Keratin (the actual material human hair is made of) there aren't too many differences. Although some brands have wider colour ranges and are more cost effective than others.

What is more important is the sources you buy it from.

On some shopping sites, the are vendors which are selling imitations of these products as the real thing. Consequently, you can end up buying a product which isn't made of Keratin and doesn't work properly.