In this article the guy actually took a stab at rating the sharpness or resolution of the spotters. You will note some are very good and some are a total waste of money no matter how cheap.
http://static.birds.cornell.edu/Publications/LivingBird/winter98/scopeswi98.htm
http://static.birds.cornell.edu/Publications/LivingBird/winter98/scopeswi98.htm









