No I'm pretty sure they're the same version and everything.
Before like a year ago there were the "CAS" version guns and the "Regular G&G".
CAS versions were built with a hybrid between Combat Machine and G&G Parts (to keep costs down). Combat Machine for the record is G&G's "cheaper" brand whereas the G&G guns were the regular G&G line (like the difference between toyota and lexus). That is all you have to worry about. There is another version that is a bit more high end than the regular G&G however G&G have refused to make a cansoft version because they don't want to dilute their brand name ("G&G Top Tech").
Since CAS now has an exclusive distributor license with G&G they have the "rec" and "advanced" lines they are pretty much the same thing as before the rec is the CAS version and Advanced is the regular G&G line.
Also the buyairsoft gun just says mostly metal, it doesn't state the upper is or isn't metal or plastic. 007 on the other hand state the upper is plastic.
It would seem you're getting the same gun so it's really your choice of who to buy from. I mean with Ken he was one of the first innovators (he negotiated to get G&G to make guns with clear lowers) and the oldest retailer in Canada.
Buyairsoft has a shoddy rep and is a relatively new kid on the block.
Again in the end it's your choice. They're both legitimate retailers and you will get your product.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE