Given that nymea runs as root in the default setup, sudo shouldn’t be needed in the command launcher plugin. There is also a kill action in the plugin which should allow you to stop it again.
So, the difference between the two is that one starts binaries, the other starts a bash and executes bash “code”.
In your case, it probably fails because python3 isn’t in the path. You might still get it to work by using /usr/bin/python3 ... instead of just python3 ....