Hello!
We're not aware of any security concern as they are layers "on top" of well tested tunnels without known vulnerabilities. Currently Russia and China users can access AirVPN, however should the need arise we strongly recommend Tor with private bridges with various pluggable transports. We have invested a lot on Tor infrastructure (see our mission), including support for an important amount of worldwide Tor exit nodes traffic, and Tor is free for everybody. No matter the obfuscation technique employed, a country or ISP can block any VPN service (and other services operated by small or average sized companies) by harvesting and blocking its servers IP addresses, a task which, on the contrary, becomes quite difficult with Tor, where volunteers all around the world set up private Tor bridges every day. https://bridges.torproject.org/
Kind regards