I agree with frfrey here, I think they're more of a hassle than anything else, you have to get the calibration solution, make sure they're not expired, calibrate the thing properly (I used to do a 4-7-10 calibration). Also the level of precision is not _that_ important, I mean, if it's 7.24 or 7.21 it doesn't matter.

If you're getting a probe I do recommend one with a temperature probe, or one with temperature compensation, as pH is a function of temperature.

And make sure the sensor is replaceable.