Recomended activity assay kits for FVIII - (Jan/10/2013 )

Does anyone know or have tried any commercial activity assay kits for FVIII

They have some activity related assay stuff here and it looks like they had more than one product if you search around:
http://www.aniara.com/mm5/merchant.mvc?Store_Code=ANIA&Screen=PROD&Product_Code=A221402

I haven't tried it, but I have used chromogenic substrates and related products from them which always worked for me.