"All connections are protected with TLS and 256-bit AES encryption. Splashtop also comes with top security features including device authentication and two-factor authentication. Plus, Splashtop’s cutting-edge infrastructure provides a secure computing environment with advanced intrusion prevention and firewalls at multiple layers."
In simple form, you control your end's security by using a secure connection, such as firewall, router, and other items. ST will secure the communication between, and your client approves the access, so you are good. Me? I also use a firewalla box to allow redundant connections, and gain security functions on my end.
Being able to use a phone to "run" a desktop/laptop is very freeing. Some will say it chains you to work, but I say it frees one to work from anywhere. Couples with multiple cell carriers and starlink, I do work from anywhere. My most favorite is processing orders while dining in a hall on Ellis Island. I imagined those who came through before, being amazed at the progress.