Please don't blame ML for features not working for you but for everyone else.
Try running FRSP without intervalometer first and follow FRSP instructions to the letter.
It's a little bit tricky to run FRSP and Intervalometer together because they "listen" to the very same trigger if default settings are used.
See details in
https://wiki.magiclantern.fm/camera_help EDIT: Just looked it up again and found 0.8 sec restriction for FRSP on 500D. Please retest. If limit still exists it looks like you could/should not use this feature for astro.
And MLV/RAW quality is the same as stills with crop mode used and MLV/RAW is working for your cam, too.