For a simple setup - I suggest you peek at Mikrotik's revamped "The DUDE"
Keep in mind - it runs on the router OS itself - and DOES NOT use windows or linux workstations to perform its tasks.
I personally like some other solutions -
Good Old Nagios,
I was using Observium but then read some postings from the Developer - who absolutely trashes WISP Operators as well as those who use Mikrotik and Ubiquiti products.
To that end - I found a great FORK to his product... (which works very well) called LibreNMS
LibreNMS is a very good tool - like many others.
It at this point really is not whats good - but rather whats good for you.
If your stuck with the inability to keep a hard drive in place - I suggest something you can run on the TIK units themselves - and that would be The Dude.
If you do want some help with LibreNMS - feel free to ask
Glenn Kelley | MCTNA, MTCWE, MTCTCE, RHCE, RHCSS
USA Based 24x7x365 Mikrotik, Juniper, Ubiquiti TAC & WISP / ISP Blind Label Support Call Center