Does fast track bypass the firewall, meaning you less secure than not using it?
Do you use it on CCR routers as well, or just the lesser ones with slower processors?
Well, somewhat.
Generally, not, you shouldn’t lose anything in terms of security, but it totally depends on your configuration. Think of fasttrack as an extremely fast implementation of a rule accepting packets that belong to a previously accepted connections, and that rule is always on top of your rule set. Honestly, that’s exactly how a sane config without fasttrack usually looks like. However please note that fasttracked packets also bypass mangle, queues and IPsec policy matcher, and that may or may not be considered as a security issue depending on your requirements and configuration.