Finally after some considerations/reviews of posts here regarding this topic i just can conclude there is no solution for this issue, however this is not a bad notice at all.

1) Certainly the product will give better coverage around all your house regarding the WIFI but you will pay the cost that Decos will not deliver full speed hired to your provider via WIFI so dont expect more that 80% hire plan speed with WIFI

2) QoS, MES option turned on/off will be very useful to help but will not resolved the issue. In that sense i suggest use only mesh activated (ON) for all mobile equipments as cell phones/tablet or notebooks, use MESH deactivated (OFF) for non mobile equipments as SMARTTvs or desktops computers once you find the best spot coverage with that you will secure the best speed scenario and no roaming.

3) Put QoS according to your fiber provider speed will help but not resolve the issue, by default value is not wrote

Findings:

a) WIFI SPEED with decos will never be same as wired cable, you will get 80% (best case) or perhaps 60% (regular) most of times. so if you are looking full speed use wired, if you are looking coverage (without important speed) use WIFI. Also most equipment works at 2.4 GHZ (no more than 100 MBPS) instead of 5GHz (no more than 600 MBPS)

b) about point 2), i found my MAC capable to surf at 290 MBPS of 400 MBPS deliver by the provider with MESH OFF and when i turned MESH ON the speed down to 65 MBPS, so due is not a mobile need i left it OFF and MAC speed is acceptable.

c) about point 3) I'm still not convinced but i left it according provider router speed. d) very important test: Try a ethernet cable (WIRED) directly from the router of your company provider and the speed must be the same as you connect via ethernet cable from main deco.

CONCLUSIONS Product ok for home but hire a fiber plan more than 400 MBPS its a waste of money if you use this Decos, certainly i will seek for other mark if you are looking for faster connections