Inefficient is inefficient, irrespective of the scale.
• "...neutrons are not a problem except possibly up close when they are moving very fast."
What happens to an atom that absorbs one of those very fast neutrons? It becomes a radio-isotope.
--Boot Hill
If I recall correctly shortly after Pons and Fleischmann's original 'cold fusion' claims either Larry Niven or Jerry Pournelle pointed out that IF 'cold fusion' really WAS fusion and could produce significant amounts of energy then because of that same effect of neutron flux you mention 'cold fusion' equipment would enable just about anyone to build a breeder reactor and any attempts at nuclear non proliferation would be mooted.
The prospect of the Al Qaidas or McVeigh's of the World producing bomb material in a bathtub is a good reason to be GLAD that the purported effect of such experiments as these is only producing so little [if any] neutron flux that it is indistinguishable from background eh ;-)?