from https://wiki.linuxfoundation.org/networking/ifb :
"The Intermediate Functional Block device is the successor to the IMQ iptables module that was never integrated. Advantage over current IMQ; cleaner in particular in SMP; with a lot less code"
surely not 
but while iptables processing is more convenient and capable, it is also significantly slower.
afaik veth and ifb avoid calling into higher-level filtering for this reason.
this does not matter for a few mbps, but for a few hundred it probably will.
maybe bpfilter can make a difference here?
Addon:
i did not want to imply that you are in the wrong using imq for netfilter capability. especially if it works for you â„¢ ...
The author of ifb allegedly also came around and regreted this design aspect, but as with the integration in cake, nobody came around to do/change it yet .