also done a few other schools before doing CSS, including CLASS with Reg Pridmore, Yamaha Champions, and Lee Parks Total Control.
now mind you, i'm 47 years old, and got my motorcycle license 4 years ago, and moved to CA just 2 years ago. i've done all these schools in a year and a half. why? i wanted to unlearn any bad habits from the get go, and embrace the technical aspect of riding and the relationship between rider and machine. i'm probably a slow A or faster B rider at an open track day at this point (or so i was told at CSS by my coach). so i'm no beginner and far from an expert.
before i discuss the track schools, anyone who has not done Lee Parks Total Control should. and while i know most of you are thinking you don't need a day in a parking lot, you'd be suprised just how humbling it can be; and helpful as you increase speed and play with traction and it's limits. Lee takes you right to the fundamentals, breaks down cornering into 10 steps in an environment where you're going 30mph - 50mph, not 90 - 140. CSS is amazing on many levels and so are the other track schools i took, but i'm glad i took Lee's level 1 and 2 before doing CSS. Anyone wants more info i'm happy to talk offline but it really helped me get things going in the right direction as i incorporated track riding and speed into my life. people i know who have taken Lee's course and who ride at the track (and faster than me), all agree Total Control was a big help to getting them going.
As for CLASS and Yamaha Champions, both great, and all three schools have many similarities and some big differences too. i'd say the good news is any one of these schools will help you be a safer, faster, and more competent rider. i'm amazed how many people out there ride powerful bikes and it's obvious they have had no formal training on how to actually handle their bikes; scary is all i can say. so any good training is recommended in my book.
as for the differences, without naming names or starting a hotly contested debate, i'd say the biggest differences i saw were around body position and what steers a bike, trail braking emphasis versus quick turn, when to apply throttle, lines, and vision techniques as you're entering and exiting a corner. Again, happy to talk offline but not looking to categorize each school and pigeonhole them in any way, just my perceptions from being a student. as i said, i liked them all for different reasons.
in the end, i wanted to be a capable rider, be in control of my bike in a variety of situations (good and sometimes bad as we all know!), ride at pace, and be able to enjoy a long tour through the twistiest roads i can find or a track day (or a ride with my wife who also rides). all of these schools were vital to that journey. now it's about more riding and figuring out what makes the most sense given the environment, speed, and elements around me.
hope this helps.