alum
They appear to be a Chinese copy of the New Zealand Pro Topline heads now marketed by RHS. The flow sheet they show is identical to the one on the RHS site.
The quality of the material used would be a concern to me. They have to cut somewhere to get that low ball price.
I have heard that you should not use valve springs that are high pressure.
I have heard that the parts that they use in their assemblies are not high quality.
I do not think they can be considered to be in the same ball park with Dart, Brodix, AFR, RHS.
For a street engine I think they are OK.
Just what I think.