I used a RB750Gr3/hEX router for nearly a year, and I wasn't terribly impressed by the software. The hardware seemed neat, but even as somebody very familiar with routing & switching I found the UI to be rather obtuse.

The other reason I decided to 'roll my own' was an in-line IDS. There seem to be 'hacky' ways to get Snort installed on the RouterOS platform, but the CPUs aren't really powerful enough to run DPI with a sufficiently large ruleset.

I also like the ability to use Ansible to manage my router/firewall. There are modules available to do this with RouterOS, but they don't seem nearly as robust and mature as the built-in Linux utilities.