I don't recommend it, it is not an official Oppo retailer, I heard people had bad experience with them before, but YMMV. If you want to, get it from oppostyle.com (probably won't be avaliable) or swappa.com.
Let me make a case for you though. If you are going to spend $500, get the Oppo Find 7a. It is going to be better overall. Why buy inferior counterpart for more?
The Find 7a is compatible with CyanogenMod and you do not lose your warranty by rooting or flashing CM. Even if you really want CM11S, I can tell you it's almost exactly similar to regular CM11. You can download the CM11S camera app and sideload it to the Find 7a. Eventually, developers will port CM11S to the Find 7a anyway, since the two devices are nearly identical.
While the OnePlus does charge faster than the average phone, the Oppo have VOOC charging which charges your battery to 70% in 30mins.
Oppo Find 7a have removable battery and microSD.
I haven't had to deal with their customer service, but from the evidence I have seen, if you have not been following OnePlus forum, I suggest you do. There are many unhappy customers who have defective devices or yellow screen issues, and a sizable amount of them have not been treated well. They are refusing to honor RMA because they save the yellow screen isn't an issue. But there can be other issues, and if OnePlus deem that it is not their fault, it will cost $60+ to ship the device back to HongKong. As for Oppo, they have services center in America that you can ship to.