Your friend is absolutely right, Bryan. Analog hygrometers do not have good accuracy, I guess +/- 10 to 20% would be common, and its accuracy deteriorates at extreme ranges. For digital hygrometers, they often list an accuracy range. For example, the one I purchased from Radioshack has:
+/- 5% RH below 40% to 80%
+/- 7% RH below 40% and above 80%
In my opinion, herpers in general do not really need to spend on a highly accurate hygrometer, as the gains from measuring 40% humidity to 41.1% humidity would be trivial. In selecting a hygrometer, I would look for durability (to withstand the tough love from herps), ease of cleaning, in addition to fairly accurate readings.
Just my 2 cents (Canadian). Hope this helps.