All of my notebooks and desktops are currently running with mismatched brands of memory with absolutely no problem. The workloads on them vary from light to intense.

If you're buying memory for the space shuttle, please buy only the most gold plated kind. For your 12 year old's laptop valueram should be just fine.

BTW, the difference in price between "premium" and "value" memory is frequently so large that it makes sense to try the cheaper kind and discard it in the unlikely event that it doesn't work as well as you like.