Some harsh criticism of the Kowas here. I've had two different Kowa sets: currently a standard black 6 and previously a 6MM. The 6MM had been heavily used and was a bit of a beater. My only complaint was the loud and firm mirror slap, and the weak film advance. Mine never broke, but you need to treat them with care. My current 6 is quieter and newer, and I very much enjoy using it. The lenses I have used are very sharp -- the "standard" 85/2.8 is sharper than the 80/2.8 on my Mamiya.
The 150/3.5 is an excellent portrait lens and can really blow out the background. The 40/4 is a fantastic lens -- well worth it's usual price $300-400. Note that Kowa is highly regarded optically in the cine industry.
Being able to swap-out a viewing screen is nice and handy. I prefer the WLF as the prism is too heavy for my tastes. Overall, I think they are a great deal, and like most older film cameras, the condition of the camera matters a lot. My current 6 is much nicer than my first one. I got a black 6 with both (black) the 85/2.8 and 150/3.5 from Columbus Camera for $200. I'm sure I could sell my set for what I paid for it easily. I recommend the Kowas, but again, stay away from those that look to be heavily worn.