The CS series pistols did sometimes have the ambi decocker/ safety. As I understand it, the later production models got this feature. The CS9 (SS) I used to have (2001 production) certainly had it.
Essentially, the CS series guns were simply SUB-compact variations of single-stack 3rd generation S&W's. Every bit as good and reliable. They were actually part of the "value line" series (so I am told) - which means that they supposedly were equipped with some less expensive parts. However, my CS9 was comparable to any other 3rd gen. I have ever seen and did not have "value line" parts like plastic sights, etc. Quality is excellent on the CS guns (just like the other 3rd gen. Smiths) and comparable to any high-end pistols being made, CZ', Sig, H-K, etc.
Regardless, they have an excellent reputation among S&W 3rd gen. guys and the value has been climbing steadily. $400 for an excellent condition example is really a very good price. A bargain, even.
As was said before, snappy recoil is the main "objection" to the CS40 version. However, recoil is no worse than any other .40 cal pistol of similar size and weight. The CS comes equipped with a rather chunky, rubber Hogue grip, which helps with recoil quite a bit. The grip, as chunky as it is, detracts a small amount in regards to concealment....and doesn't fit everyone's hand. (That's the ONLY reason I no longer have my CS9.) Accuracy tends to be quite good, like the other 3rd gen. models, notwithstanding the fact that the subcompact size takes a bit more getting used to. Some people claim that the CS series guns tend to shoot low - but I am convinced that this is an operator issue, in combination with the grip (which as I said, doesn't fit everyone).
Reliability is excellent, as good as any other 3rd gen. Smith. Parts will become a problem in future, eventually, But, as the guns are VERY reliable and do use some parts common to the other single-stack 3rd gens, I don't think this should be a major concern (perhaps in 10-15 more years).
Overall, my take on the deal offered to the OP : If I was a .40 cal guy and if the grip fit me better, I'd be ALL OVER that deal myself. As the collector value of the CS guns is climbing steadily, he probably won't lose $$ on it. They are excellent carry guns and excellent shooters, so if he uses the gun regularly, it will be a real pleasure. In short - BUY it !