This is true classic, the day my CS-600P arrived, I went on EBAY and within five seconds, I found the chain brake that had been eluding me for over a year, and at about half the price it was when available through parts sellers.
I bought it, and installed it last night, and am now a three-saw operation, lol. The old Echo CS500 has a new bar (its first in 30 years) and chain, and the CS-300 has its first new bar. The chain brake on the CS 500 wasn't as simple to install as it would appear, but after finding the right sequence of expletives it got on there and works. Haven't yet started the CS-600P, but the snow melted today, and if we don't get some soon, I might give it a whirl.