SHM in STC and STSC are completely separate apps and their status is not shared between the two apps. So if you use SHM in STC for example, it will not work with Automation/Custom Rules in STSC except for smart lightling rules. Also, geolocation in STSC can not perform unlock door or open garage door or set SHM - actions you can do with geolocation in STC.
Best advice is to use one app and at this point, STC is the recommended choice.
And be careful if you set up alerts in SHM in both apps, you will receive two separate alerts. This confuses some users who clear the alarm in one app but continue receiving alerts every hour because they did not dismiss in both apps.
Last note, you can not use webCoRE to set SHM in STSC.