510 but are you sure you want to deploy a 5Ghz device, only 5ghz devices will connect
210 is 2.4Ghz anyone connects

I am trying to extend wireless coverage for about 300' to 400'

CPE210 can easy cover this distance. But notice that client devices such as smartphones/tablets/laptops may not be able to transmit back to the AP when there are obstructions in the way.

Thanks Dannymarc and Zetm.
I didn't think about the 210 would serve both 2.4 and 5 ghz. I guess I was thinking 5 ghz for all the new technology that people use and take advantage of it. Seems they would have one that would do both since they have routers that do both.
What about the TL-ANT5823B, I don't have to go very far from my router to cover the area, I just need to get it to the outside of the building. Wouldn't they do both 2.4 and 5 ghz?