Both can be used in Space Travel as well, the ESA (European Space Agency) has launched a variety of Ion Propulsion Sytems into Space. They are slow but they a 'free' from and energy perspective anyway. I like both of these names Crodo. They may not be desirable at this very moment, but they will be. My advice is to reg both of these for 10 years and tuck them under your bed alongside any other personal keepsakes.
If you really must have an 'appraisal', $100 to $500 each.
Regards.matt