EM Drives

Can someone ELI5 the issue here?

Eg isnt is just "capturing" the electrical (either nuclear or solar) and the "opposite reaction" actually occured "previously" and is stored energy (or store momentum as in this case).

I dont get what the big deal is here

- http://www.sciencealert.com/the-impossible-em-drive-is-about-to-be-tested-in-space

- http://emdrive.com/