Hi Francis,
Yes the eye is to indicate wether RingRoost can reach your SIP device.
The Zoiper App may run into some connectivity issues if you are on the go. I would recommend using our mobile App
https://www.ringroost.com/user-manual.php#mobile-phone-app for your mobile device, it makes/receives calls over your cell network which is generally going to be the most reliable.
FYI: You could also use the mobile app as fallback if your cell phone/Zoiper can not be reached.