How we use Prometheus QoS in Brevnov: 

1) /etc/hosts

1500+ IP addresses are asigned either guaranted speed classes 64, 128, 256 
and 512 kbps, with various HTB ceil rates, using "via-prometheus-" keyword.
Some of IP addresses are set to share connection speed with internet 
gateway using "sharing-" keyword.

2) /etc/prometheus.conf

There are daily traffic quotas defined using "magic-relative-limit" value
se to 8. This translates into 48h quota 1 GB for 64 kbps lines,
2 GB for 128 kbps lines, etc., with unused credit from day before yesterday
stored in /var/run/prometheus.credit. Soft quotas (fair use policy) are 
applied (resulting in lower HTB priority) even before hard quotas are reached
(magic-relative-prio set to 6, which is less then magic-relative-limit set
to 8).
 
Daily limits are applied by running prometheus every day at 3:00 AM. Between
3:00 AM and 6:00 AM, there is QoS free period, enabled by "qos-free-delay"
value set to 10800. However, yesterday's data transfer statistics are kept
in memory while prometheus QoS is iddle in this sleep mode. 

Undefined IP addresses share 32 kbps guaranted and 64 kbps maximum speed, 
set using "free-rate" and "free-ceil" keyword.

There is QoS-free zone defined using "qos-free-zone" too be 10.0.0.0/8. 
This allows for example easy management of gateway from inside this range,
or remote management of entire network after ssh to gatway and then another
ssh to this zone.

We run HTTP proxy at port 3128 of LAN interface of internet gateway. This
proxy is inside "qos-free-zone". Because of "qos-proxy-enable", 
"qos-proxy-ip" (which is actually IP/number of bits of netmask) and 
"qos-proxy-port" settings, this port is excluded from QoS-free zone.

3) NAT

Both symetrical and asymetrical NAT is defined by another script file, in
iptables nat table (-t nat). Prometheus QoS uses only iptables mangle 
tables (-t mangle), see FAQ.

4) /etc/crontab and related files

Every hour, we run prometheus with -p switch to generate preview. On system
boot, we run prometheus with -n switch to skip QoS free period.