Don't get too excited mate, its just a car forum.
Yes you are right about the mixing, but look at it this way, before the art of commerce was established, corn flakes were made by Kellogs, and only John Smiths sold bitter. Anti-freeze is anti-freeze, it lowers the freezing point of the water in your cooling system, that is the prime objective and you should not be fooled into thinking that you 'have' to use a certain product, when the cheaper alternative will do.