@Kevin_Z Please help.

I bought TL-WA850RE and connected perfectly with my router. My base router gives me 100mbps, but the wifi extender even in the same room gives me 20-30mbps. I have moved it around still the same speed.

What am I doing wrong?

@Apple85 you're doing nothing wrong. The repeater doesn't have the speed indicated on the packaging. I had the same issue. I don't know if it's a product bug or just a very very bad product. In both cases, the repeater is useless. I sent it back. You should consider doing the same.

@Malou which one do you suggest, which will have almost same main router speed?

@Apple85 very good question. I have absolutely no idea. Let me know if you have one that works

@Kevin_Z 

I had a Re200 in 2015, worked fine I remember, now also doing it's job in my parents house.....

So I bought a RE300 2 weeks ago, connected easily with WPS, twice for 2.4 and 5.0GHz.

Upload speeds seem very acceptable, I have 30Mbps upload max, upload speeds through the extender come up between 25 and 29 Mbps, 

but the downloads come no where near my max of 70 Mbps.

So I came to this support site, and checked the standard suggestions, I have no irregular set up, so all should be good to go....

But, I have no clue what else I can try...

The first extender I got, connecting to the extender took up to 35 seconds, sometimes just below 10 seconds, but no where near the < 1 second when I connect to my modem...when testing speed on the ookla speedtest site, came to about 30 Mbps for a second or so, then quickly slowing down to between 2 and 7 Mbps... totally unbelievable...(for the 5.0Ghz). The 2.4Ghz came to about 18Mbps, also not very impressive, and looked very erratic. I did a reset, checked some settings in the tether app, tried several things, but the 5.0 Ghz downloads were insanely low.....

So I sent that one back. Thinking this should be some sort of "production error", I wouldn't believe the product would normally be bad, so I ordered another one.

Got that one yesterday, set up again easy with WPS, speeds are better, but still, I'm very disappointed.

My old aliexpress cheapcheapcheap 2,4Ghz wifi extender shows a "steady"  23.4 Mbps download and 29,1 Mbps upload....

(and even connecting to that one takes less than a second!!)

When connected with my phone directly to my modem, I get up to 36Mbps download(2.4Ghz) and up to 73Mbps(5.0Ghz)

The TP-Link RE300 is not steady,  I tried several different locations within the ookla test app,

I put the extender in different sockets, different distances from my modem....  but no reassuring data is coming out all of this.

I also noticed a couple of times the 5Ghz led was off. Even one time when I was connected and using the Tether app.

And connecting to the modem takes 5 to 15 seconds, sometimes longer.... 

So the strange thing is, that the second one I got, seems better than the first one, concerning the download speed, but still not good.

Can anybody tell me it can get better? And how?
Let me know, otherwise I will have to send this one back as well, and am not sure there will be TP-Link for me in the future.

thanks,
Wil

P.S. I also connected and tested with different devices, laptop and tablet... als not reassuring the quality...

@Kevin_Z 

ok, was reading some more on the internet....

so in general -I was not aware- an extender about halfs the speed of the internet.... ouch

in my case 70Mbps would be reduced to about 35 Mbps.

still ok for it's purpose.

I read more on the settings, and found out about the option in the Tether app, to set the High Speed modus to manual.

So I set it to use only the 5GHz band, 

and what do you think... now all seems as to be expected....

tested again several times... download speed goed up to 35Mbps indeed, 

and test is steady, not like the test were before...

so it seems this extender needs to be configured as desired...

I'll give it a try...

@rajub  that was also my question. Thanks a lot, I got my solution

@Kevin_Z My problem is my upload speeds are perfect but download speeds are cut in half. This one time my dl speed matched that of the router but then it throttled itself back to half speed in like an hour.

  @Kevin_Z 

I have encountered the same issues. 
500Mbps vs 37.38Mbps on TP-link after I followed all steps. I have tried to call for support for an hour but there was no response. Any ideas? Should I replace? Thanks