FWIW I'm using hnyman's stable 19.07 for my parents' low-tier Crapcast connection (100mbps down, 5mbps up), and I was able to significantly reduce bufferbloat by using SQM with "cake/piece of cake" setting. IIRC I actually took it from grade F to grade A/B variation according to DSL reports.
The firmware is good enough to enable SQM on such low-speed connections. Up to 200/200 up/down it would work. Maybe 300/300.
Remember that software acceleration has to be DISABLED for SQM to work.
For higher-speed SQM you'll have to deal with less stable NSS firmware by ACWifiDude, and you'll have to use NSS-accelerated fqcodel SQM there which currently can only be configured via command-line/file editing, not via UI.
Software acceleration has to be disabled for that one as well, because it is currently interfering with hardware acceleration, which brings greater benefits and is enabled by default. At least, that's what the posts suggest: https://forum.openwrt.org/t/ipq806x-nss-build-netgear-r7800-tp-link-c2600-linksys-ea8500/