@Enri 

The extender will not be as fast as the router because of how both work. You would need an Ethernet cable from the router to the extender, then set up the extender as an access point if you want to get the best speeds possible.

The 2.4G looks fine, but the 5G seems a bit slower. In general, you would expect around 50% depending on the signal and speed the extender gets from the router.

Try repositioning the extender in a different area since itis already configured and see what performance you get.

What you can also do is to set up the extender in high-speed mode (one band connects to the router, the other band connects to devices): https://www.tp-link.com/support/faq/2479/

Please also make sure the extender is running the latest firmware: https://www.tp-link.com/support/download/re305/#Firmware

@Tony 

Hello Tony!

Hope you can help me. I have the same issue of this post, although I'm using de RE305 as an AP.

I tried with different configs suggested by TP-Link in other threads , channels and so on... and nothing seems to work. 

Using 5G from router or another AP (Mirastar): 400 mb. 

Using 5G from RE305 as AP: 100mb. 

Any help, recommendations o tips?

Thanks. 

@Crisfm 

The RE305 has a 100 Mbps Ethernet port so you will not see any speeds higher than that as it is a hardware limitation.

I'm having same issue. It worked well for a month. I changed nothing in my setup but it became very slow. Updated firmware and everything but no luck. Please fix it and release firmware update soon.