Have you ever been told by a professional who is rendering service to you that you need to use the entire family of products to achieve a synergistic effect? I have, quite a few times. Let me tell you why they are mistaken.
This is old news, sort of a sales pitch/wives tale invented by some marketing genius to get you to spend more with their company. Almost all of the different families of products contain somewhat similar ingredients and the are also manufactured by one of the few major manufacturing facilities that exist in the USA. Let me rephrase it this way, same general ingredients, same manufacturers, different labeling and packaging.
No all products don't contain the same ingredients for example, there are good ingredients and there are cheap ingredients. Companies like Suave and Pantene use cheaper, harsher and more abrasive ingredients in their products to produce their $3 shampoo. The results you get from these cheap ingredients can be dryer hair and skin, breakouts along your hairline, a waxy build-up in your hair (ehhhm Pantene) or severe drying of your skin. Companies like Alterna and Kevin.Murphy use more costly ingredients which results in a refined product. They tend to eliminate synthetic preservatives (parabens) and GMO (soy, corn) so your body and our environment doesn't have to pay they price. So if you use a Suave shampoo it will not make you Alterna conditioner any less effective, but trust me that Suave shampoo is making your color fade way faster and isn't benefiting the health of your hair and scalp at all.
So when you are out choosing products just keep in mind what options are the most important to you. Is it cost? Is it the quality of the ingredients? Are you looking for a targeted result (stiff, soft, color protecting) Is it the design of the product (how it fits in your hand, stays upright in your shower, dispenses easily) Whatever decision you make know that your product is working despite the fact that you haven't purchased it's companion or two or three. I personally like to try 1 to 2 items in a line before I will commit to purchasing any more. Suit yourself.