Motul is a manufacturer for lovers of the better product. Their high quality lubricants are used in the racing world for a reason. They are developed with the latest technology and extensively tested to ensure they continue to perform in the most demanding conditions.
And while that's true for all Motul products, this Factory Line DOT 4 Racing Brake Fluid 660 is the high point. This brake fluid is specifically developed to meet racing conditions. Carbon, steel or ceramic braking discs generate more heat and that requires a higher boiling point in the brake fluid. Motul Factory Line DOT 4 Racing Brake Fluid 660 is a fully synthetic polyglycol-based brake fluid developed for racing motorcycles, although it is perfectly useable in conventional brake systems.
You can always downgrade. Upgrading will be difficult in this case, because there aren't that many conditions that this brake fluid can't handle.
Mixing with all DOT 3, DOT 4 and DOT 5.1 products is allowed, although this will obviously negate the added value. The extremely high dry boiling point makes braking safe and secure, even in extreme conditions. The same is true for the wet boiling point, which is especially important in wet or humid conditions.
In racing situations brakes are subjected to extremely high levels of thermal stress, so it's advised to check the Motul 660 at least every second race and replace it when necessary. It's equally important that you store Motul 660 in a sealed container and in dry conditions.