@nojak 

You need a powerful CPU in your router to use SQM in a fast internet connection.

If your speed is below 150 mbit, get an Ubiquiti ER-X, and flash it to OpenWRT.

Faster speeds require x86 hardware (even old will do) or a RPI 4.  

@Erik I have a Turris Omnia. SQM on my Internet connection works very very well. 
However, wifi is still an issue. The buffering on the EAPs is noticeable, even at "good" PHY rates, as real throughput is a lot less than the PHY rate and can be close to my Internet speed. Then we add in things like backups to NAS, and wifi congestion/bufferbloat is real.

Sadly it seems that too many apps do not tag DSCP properly, making it hard to use that.
 

See the link I posted in the first post. Just talking about wifi.

eero now supports SQM on wifi. Hope TP-Link would add this to EAPs.

@nojak 

Would it be possible to set up a local netperf server and run https://github.com/openwrt/packages/blob/master/net/speedtest-netperf/files/README.md to get some figures?

BTW you may want to try OpenWrt on your EAP225: https://github.com/svanheule/openwrt/releases/tag/eap225v3-9318c00

EDIT: Added note about OpenWrt

@Erik I was thinking of netperf as well. One day. 
I'd rather not install OpenWrt on an EAP; I lose all the Omada controller features including roaming. And I have most issues between my MacBook and an EAP245, just because it is the closest EAP to my laptop.

@nojak 

My setup may be a bit different - one EAP225v3 and the older EAP330. I used to run the Omada controller app, and much enjoyed managing EAPs using the tp-link mobile app, however the setup was never stable - never understood why. In an act of desperation, I changed management mode to stand-alone mode and then the wifi experience got a lot better. Have you tried your setup with central management?

Roaming never got supported by EAP330 - so I can't comment on the potential benefit of that feature, but if you want to improve roaming another option could be to try playing with lowering transmit power.

OpenWrt may support the fast-roaming feature (not sure about -k and -v standards)

https://forum.openwrt.org/t/802-11r-fast-roaming-in-luci/11730/35

https://www.reddit.com/r/openwrt/comments/515oea/finally_got_80211r_roaming_working/

@Erik My Omada controller on a RPi 2 works very well. Fast roaming on mobile devices (MacBooks don't support it). 
Tx power already optimized/lowered on my 7 (soon 9) EAPs; that was the first thing I did. 😁

@nojak 

Wow! Soon nine EAPs! Do you live in a palace? 😂

Here's something that may make the wifi experience better but most likely not related to your initial question:

https://forum.openwrt.org/t/acceptable-wifi-latency-jitter/59655