Is Skiff trustworthy? - eviltoast

I’ve been using skiff. com for sometime, as they claim to be a fully privacy preserving app suite like GApps or proton. One thing I like is they provide 10GB storage even for free accounts, where proton eventhough much bigger provides only 500MB.

But that got me wondering… Are they trustworthy as proton? Is there a chanve they end up being a honeypot? Does data actually gets encrypted before sending to the servers in a trustworthy way?