I bought the Banana Pi specifically to act as a TOR relay. The set up itself was surprisingly easy (instructions for the raspberry tor relay apply for the Banana ). The relay was set up with a 2Mbps bandwidth limit and has been running for approximately 10 days, with an average throughput of 260Kbps and peak CPU and RAM usage of 60% and 12% respectively (peak upload/downloads of 3-4 Mpbs). I'm delighted with the performance of Banana Pi and I've just ordered a 2nd one for my next project.
About TOR relay device, you could check my own HackaDay Prize project : https://hackaday.io/project/2040
It made its way to the semi-finals, and I'm actually porting it to the Banana Pi (looking forward to BPi-R1). Sources and documentations are also coming.
If you like it, throw me a skull