Stirlingtek has a very good reputation and should be fine. I haven't used their LP-E6 yet, but have used some of their BP511A, which if anything were superior to Canon's.
When I bought my 5DII and 7Ds, there really wasn't a choice... Canon OEM LP-E6 were the only fully compatible batteries. Initially they were hard to find and sellers were taking on a premium price! The first non-OEM knockoff LP-E6s were made without all the same circuitry and couldn't even be charged in Canon chargers. I didn't have much choice and ended up buying LP-E6. Since then it seems the third party battery makers have fully reverse engineered the LP-E6 and are selling fully compatible versions at good prices. On a positive note, I didn't need as many LP-E6. Where I always carried two backups for each BP511A, I found the newer LP-E6 were good for so many more shots, plus recharge fast enough, that I only needed a single backup for each battery.