When fasttrack feature was introduced there were numerous reports how buggy it is, and also several updates on how developers implements fasttrack further.
Now is the question: is it safe and useful to enable fasttrack rules on the router which used mostly as VPN concentrator (and which has 80-90% busy CPU)? In fact the firewall rules are pretty simple: general forward and input/output rules to drop common evil traffic and allowance for VPN-used ports and protocols.