If you want to use it just for migrating, both ways (just booting it or installing it) will work with /e/OS. If installed (= embedded into the boot partition) TWRP will simply get overwritten next time you update /e/OS, because /e/OS will then restore its own boot partition including its own /e/OS recovery.
SAI for exporting and installing all your important App APKs (because some Apps have split APKs, which some other APK exporters can’t handle correctly), and MyPhoneExplorer for transferring contacts, SMS, calendar, pictures, the whole Internal Storage if you like (HowTo and FAQ, and here’s how to transfer SMS as it’s not very intuitive).