Who else believes that its a hair MUST to use the same brand and line of conditioner that matches your shampoo? but that isn't the case. Truth is you can do whatever you want with a mix of products.
It is however known that you'll have greater results if you stick to a coordinating shampoo and conditioner, but in general, simply staying with the same brand can grant you good results.
It's all about knowing your hair. Already have volume? Then stay away from volumizing shampoos. Lacking volume? If your hair is oily, greasy, or is generally lifeless at the root, look for a really good volumizing shampoo.
If your hair is dry or damaged, it may be better to invest in a really good, hydrating conditioner and find a cheaper shampoo.
If your hair is generally normal or doesn’t fall into the above categories, always default to a higher quality conditioner over shampoo.