I've owned two CS-670's and a CS-6700. They are very well built saws and will provide many years of trouble free service.
The con's are lackluster for power production, OK, but not on par with a Husqvarna 268xp, 272xp, or 372xp, for example. They also oil the chain all the time.
None of mine were overly happy with 24" or longer bars on them, OK with a 20" bar. For some reason all three had a pretty narrow power curve, decent mid-range, but not overly impressive high RPM power. If I tried to lean any of them up to get them to RPM they would stall against the clutch too easily when you started "pushing" them hard.
I sent all three down the road and went to the CS-590/600P/620PW platforms instead. They are a much better design, better power to weight, inboard clutch, excellent anti-vibe, ergonomics, and broad/smooth/flat power curves.
Now when Echo builds a 70-75cc saw on the CS-620 platform it will be something that will get my attention for sure......Cliff