i would not use this swing with my chins.
look at the way the chain is attached - right at an area that is easily chewed. within a day (or a half day if your chins are house beavers like mine), that area will be chewed right down and the chain will no longer be attached to the swing. swing will be hanging dangerously in the cage.
fir is safe as long as it is organic/kiln dried/doesn't have bark, from what i have read.
items from china are always questionable. many times when natural products (wood, etc) are brought in from other countries, it is mandatory to spray them with chemicals. not good for chins.