Adding wireless surrounds bad idea or works well?

My main system is 2ch but I've been toying around with Atmos since my house has built in speakers for Front Height and surround.  It is impossible to run wires to other rear/side speakers.. Are these wireless kits worth it? Any good?  Is there not a huge timing lag?

Wow no opinions..  I should have added that I'm considering a cryogenically frozen power cord to the wireless receiver in the rear for added transparency and less latency.  
I've been wondering the same but just wireless for rears, I have main speakers and center but don't want wires unless there are no choices. I've googled but haven't found a solution that gets decent reviews. 

Yeah @trevanian, good wireless rear speakers would be such an awesome thing, I'm surprised too that more people have not tried them or weighed in on the good/bad parts.