splashtop is loose and unencrypted. It is intended for showing video on remote desktop, so they removed encryption and anything else that could slow video processing.
If you are using this in a home, trusted, network and not showing anything sensitive, it is fine.
If you are at school/work/public network, or are looking at sensitive material, then use something else
There are several free vnc clients for iphone, several free RDP clients for iphone. I use Teamviewer professionally, but that app is $99 in app store