In your opinion, are these "full spectrum" lamps what they claim, and
which do you think is the best value?

There is an entire book devoted to this subject.  "Light: Medicine of
the Future" by Dr. Jacob Liberman (Bear & Co 1991, $17).  Dr. Liberman
asserts that exposure to direct sunlight for an hour a day will have
profoundly positive health effects. Full spectrum lights are
recommended inside the house but sunlight exposure is the best.  He
has a close affiliation with Dr. John Ott, who wrote the forward and
also sells the leading brand of full spectrum lighting.  Book reviews
on Amazon will give you a good understanding of the subject. 
Currently many used copies of the book are available for under $5.

Perhaps this will be helpful to you.

Home and Garden Guide - Home and Garden Guide
http://www.cleaning-guide.com/full-spectrum-lighting.html