@David-TP Thanks for your reply!

The hardware of Acher C20 that I´m using is 1.0 version.
As I said the total bandwidth from my ISP is 500 Mbps of download and 50 Mbps of upload, so when I tried to set de Deco QoS, I use that exactly values.
When I said “It doesn´t work as supposed” it is based on comparison between the C20 bandwidth control, because when I set the C20 QoS in 60/60, for example, there is a limitation in that speed (I checked at Speedtest.com), but when I set Deco QoS in 200/30, e.g, that limitation does not work.
Why this occurs? The behavior of Deco QoS and Acher C20 QoS are different? If so, can you give me an advice in order to keep using Deco, but free of buffebloat? 

Thanks again.

 Hi @David-TP,
Answering your first question… Yes, in that situation the speedtest from Deco X60 was over 200m/s.

I did the suggested test, and for the first evaluation the bandwidth control worked, now I will perform additional tests for bufferbloat evaluation in order to find the right bandwidth setting.
If that works, I could use the guest network as the main network. Is it correct? Anyway, considering this configuration I think that if I use the ethernet cable plugged into DECO, the bufferbloat issue will still occur. But, even so, your suggestion is a considerable solution.

I have another question, is it possible to do an Internet speed test on the X60 v3.0 connected to my home network when I am in other location, e.g, at work? I'm asking because when I open the TP-LINK Wi-Fi Tools app at work it searches for a Wi-Fi network.

Thanks again.