Did a quick research on this software(Geph) and its creator. I”d say this is indeed somewhat trustworthy.
Here are few reasons,
First and foremost, The Developer/Creator is called nullchinchilla, Dude got some balls. He legit posted all the codes of this software on Github.
Secondly. I did check some of his source codes. Nothing arouses any suspicions for me.
Thirdly, The company is indeed registered in Estonia which does have a strong privacy protection records.
Well overall. this dude is pretty intriguing. He kinda reminds of clowwindy-sama (the legend behind shadowsocks) but with less weeb infection lol.