I recently purchased AirVPN and it feels indeed very mature and tech-savvy service. However, I can't get full speeds, even though I have tried common tricks.
I use an USB LTE mobile broadband stick, so my MTU is not (maybe) 1500 normally. Speedguide.net's shows that MTU is 1440 and MSS 1400, when I don't have the VPN connected. Because of mobile connection, my speeds differ from time to time, but currently I get download speed of 15 mbit/s and upload of 45 mbit/s (this is a result of many concurrent users at the same cell tower, but this is not the reason for low speeds, naturally). My OS is W10.
I have tried both UDP and TCP modes and multiple ports, but speeds at AirVPN are DL 5-7 mbit/s and UL 10 mbit/s. They are significantly lower than without VPN. I increased the buffer sizes for both RX and TX to 256 kB and 512 kB, but it made not apparent difference.
I tried the connection without Eddie and used the latest vanilla OpenVPN client with generated ovpn-configs, but speeds remained low.
What is the most interesting part, is that my ISP is not throttling the connection. I tested this with another VPN service and their UDP protocol connection gave me DL of 12 mbit/s and UL of 39 mbit/s. I am sure there is some parameter which makes this difference, but what is it? I also trust 100 % at your infrastructure. Every time I connected to AirVPN servers, there were at least 850 mbit/s of bandwidth, so the problem is in the configure, but where?
By the way, what I wrote about MTU, I didn't find any difference between AirVPN config and the another service's configc files, what comes to mssfix or related.