Didn't want to start a new thread. I'm in the same boat. Just bought the 600ex rt a week ago.
Is this a good battery pack to use?
It appears to be a B&H rebranded Pixel pack. They are good packs, I have several of the Pixel version. If you are using that, or a similar, pack you will also need 24 rechargable AA batteries, Eneloops are very good. Especially the new higher ampHr rated ones. And at least one really good charger/conditioner. When its all added together, the Cheetah 4500 is about the same price.
As discussed above there are other, more attractive options.