10x is plenty big enough and far easier to see thru than a high powered glass. the higher the power the more steady you need to keep your hand that's holding it but with 10x you can still see the entire "mushroom" shape and its color change very easily, even with the shakiest hands.

i get mine from ebay for about 5-8 bucks each...15-20 for the metal cased ones with a built-in light.