I use Open Explorer everyday so I don't mind supporting the dev and the hard work put in.
I have a Asus Transformer Infinity (TF700T) tablet that has 2 sd positions, the micro sd on the tablet and the sd slot on the detachable keyboard. Aside from the native file expolrer, open explorer beta in the only one that makes both sd positions easily available and it does it better then the native app. So you are welcome to my contribution. Now if you could make it so I could run apps from my sds I would give you 6 stars.
I love your Open Source file manager idea. The problem is that it keeps crashing when selecting a file. Also, for unknown reasons, some files when selected, the menu does not allows renaming the file. I do hope you get time to solve all this issues and rule the only true Open Source File Manager on Google Play. I am not requesting a refund, I trust you.