Don't mix up SA expansion with the Enhanced client.
I *knew* they were making a mistake giving them both the same name.
The client is free, as KR was. The expansion we pay for. From August 14th - 23rd you can log in to the shard with the expansion on and have a look at the new content. It will be on sale from Sept 8th.
You will be able to visit the new lands and access all the other new content, once you've paid for it, with either client, and if you don't buy, you won't be able to access it no matter which client you use.