With any digital (or analogue) hygrometers it's worth taking the time to test them, you'll find that most read a few % out, some a lot more, if accurate humidity is important then whichever one you get don't trust it without calibrating it first!
There's a very simple test you can do called the "damp salt test", put some salt in the bottom of a glass and dampen it, it should be just damp not wet and sloppy. Then place the sensor in the glass so it's suspended just above the salt, and cover the top of the glass with clingfilm held in place with a rubber band.
Leave it overnight, in the morning it should read 75% if it's accurate. If it's just a few degrees out you can allow for that, but I've tested some hygrometers that read up to 40% out!
FWIW the best of the cheaper models that I've used is this one Thermometers4U Online Shop - product details