I have done a number of Astro Starts with a manual transmission. It’s imperative that the safety circuits (dome light and parking brake) circuits are solid. I used them on a couple manual transmission cars I owned as well. Never had a problem. Just need to remember to arm it correctly prior to leaving the vehicle, which makes it a pain when you were not expecting to need it. I just completed the install of a computational remote start on my 67 (4R70W automatic). It was simple to install and start on the default settings, but the custom config settings with a remote is a pain in the ass.
First Edition 4dr
1967 Bronco
1993 Mustang Notchback