Most people did sign up for KMK. Everyone in my class did except for myself. Most people on the optometrist facebook group admitted they used KMK for a question of how to study for boards.
Some friends valued it, some swear by it, some classmates said it wasn't necessary and wasn't worth the money. I didn't take KMK like I mentioned above, and I thought boards were cake. An upperclassman gave me his KMK books to borrow, but I hardly read through them because I found it not a fun read.
In the grand scheme of things, the price of the program is probably equivalent to 2-3 days work of pay when you become licensed, and if you want that reassurance that you will be on track to getting licensed as soon as you can, all the power to you. Honestly though, why would you pay for a course when you already sat through the classwork and you have your own notes? That's why the cram course never appealed to me. But I suppose I missed out socially because I wasn't in the KMK "gatherings" with the other 99% of my class.