Answer is Yes, this feature will help, however take it with a grain of salt as there are other elements out of your control, see reasoning below.
User guide download here
From the guide there are two key statements:
Prioritization settings are applied only to traffic that is uploadedto the Internet. The router cannot control the quality of the trafficafter it reaches the Internet.
Caution: If you specify a maximum bandwidth that is too high, therouter cannot apply priorities correctly, and prioritization problemsmay result.
Checking elsewhere some people ran into issues when defining the media prioritization config, which I don't think you are running into, however this link might be useful.
Unfortunately the User guide is very basic in providing details of how things work under the hood, and my thoughts have indeed been confirmed, how to quantify the amount of traffic that is being prioritized and how to further understand more in-depth the inner workings of this type of setup.
The information below came useful:"it's pretty hard to objectively quantify the effect of the 'Media Prioritization' settings"
On this last hyperlink there is also discussion about the service being traffic shaping and not QoS in case you are very picky on the use of terms.
From the Lynksis community support you can broadly define the workings as such:
Downstream bandwidth is the maximum amount of bandwidth your ISP provides you.
Devices listed a High Priority will be given what they require from the Downstream bandwidth.
Devices listed as Low Priority are given what bandwidth is left over after the High Priority devices.
All devices never exceed the Downstream bandwidth maximum. So if you set it at 512 kbps all devices regardless of their priority will never get more that 512 kbps.