i think that you can have a better power efficiency with raspberry pi 3 cluster instead of those mining stick, since Raspberry pi has just 5~6 watts per modest (AFAIK), where there are at least 24GFLOPS per node, should do around ~10 GH/s per node. hope i didn't make it wrong.
Sorry to burst your bubble, but GFLOPS (Billions of Floating Point Operations per Second) have nothing to do with GHA (Billions of SHA256 Hashes per Second). The SHA256 Hash operation involves numerous logical operations (And, Or, Xor, and Shift) on binary data. It has absolutely nothing to do with a Floating Point Add, Subtract, or Multiply. The lowliest 333 MHS (i.e. .333 GHS) Asicminer USB stick from 2013 is many times faster than the fastest CPU mining on any general purpose processor (e.g X86 or ARM in the Raspberry Pi). You might be able to find CPU mining software that you can compile and run for yourself. For BTC mining with the SHA256 at the center, an ASIC is the only cost-effective way to mine Bitcoins. This has been true for at least 4 years.
The ASIC miners of today are so streamlined and specialized, the ONLY thing they can do is the SHA256 operation. They are 0.0 GFLOPS (couldn't do a Floating Point Operation of any kind).