Not a good idea to mix different brands -- especially if Brand A is say mix ratio of 1:5 and Brand B is say 1:2. ( Hardener:Resin). You possibly might be successful with 2 brands with the same mix ratio. Like Brand A 1:2 and Brand B 1:2.

Epoxy works by the principle :resin and the hardener linking together chemically ( a crude example would be --like velcro).

The chemical compositions of different brands are different .

Say you use the correct ratio of hardener from one brand for a particular resin of another brand , there is no guarantee that the all the links will bond chemically to create a hard inert mass. When the chemical linking fails youo would just get a semi-hard end product or worse a soft mixture.

Dont waste , IMHO, the effort trying to get it to work .

Hope this helps.

Cheers

Prasad