Effectively suggesting and recommending take home hair care product is vital to salon success. There is zero room for debate on that point. The more product you can move, the more loyal your customers will be to you and your salon. Period.
"Guys are buyers, women are tryers" has always been my mantra. Women will ask about small sizes and samples. Guys want to buy big and be done with it. Guys need far less variety than women seek in hair care options.
Rather than try to learn a lot about a vast number of products, I have always advocated my core item concept. It is kind of like my version of the 80/20 rule of guy hair care: 80% of your guys will be completely satisfied with approximately 20% of the men's hair care product offerings on the shelf. Do what is needed to be rock solid in your use and understanding of these limited number of core items.
Likely one shampoo, one gel, one paste and one pomade covers the lot of them. Keep it simple. A broad application shampoo can be offered up to any guy. A thin and fine hair shampoo will be great for the thin and fine hair guys and will also deliver for the thick and curlies, too. Do not over think it. Most guys do not keep their hair long enough to have conditioning issues. They cut it off before they have time to trash it. Their main concern is getting yesterday's styling product out so today's can be put in.
Gel, paste, pomade: for any guy's hair type, two of these are pretty wrong and one of them is pretty right. Figure it out. The best kind of product knowledge is USEABLE product knowledge. This is product knowledge gained from USING the product. Get it out of the package and onto a head. In an instant you will know exactly what it does, how it feels and how it makes the hair look. If it is the wrong product for that hair type, shampoo it out and try the other product. Make a mental note and do not try that combination of hair and product next time. Learn from the experience.
From time to time, new items are introduced. Experiment with them and add them around the core of your product information, or not. With a limited number of core items and only a few combinations you will become your salon's guy-hair product expert in just a few heads of hair.
Keep it simple.