There is nothing equivalent in size to the Devo 6 from other manufacturers. This reflects the fact that Walkera transmitters are usually bundled with their helis rather than sold as standalone transmitters. There is now an increasing number of people using their Devo transmitters to control the Nano CPX. Walkera will be watching the situation the situation carefully because they don't have anything equivalent to the Nano CPX at the moment.
Here is a video of a RCG member using his Devo !0 to control the Nano CPX. This looks good bearing in mind that the deviation firmware for the Devo 10 is an Alpha release. However, I still think it is sensible to fly helis that are at or below the 130 size.