I have been using this thermometer for the last 5 years and it is as good today as it was on the day it was purchased. It is used daily in the course of my work and I have another one for home use too. It is singularly the most essential item for any home health kit and no parent should be without one, especially with the current pandemic of swine flu and onset of Winter ills. The readings are at least as accurate as the traditional mercury in glass thermometer but its versatility of use across the whole spectrum of ages, from infant to adult, make it the clear first choice. The memory function for the readings is also useful to monitor progress at home but there is only one so if you'd like more go for the 4520 which has eight.
The covers are best bought in bulk and obviously have to be changed after each patient for professional use, but at home when used on the same patient each time a simple wipe with a damp cloth will be sufficient, meaning that one cover should last the duration of the illness in such cases. For maintenance just wipe over the sensor tip with a damp cloth between uses and storage and that should be enough to keep it in tiptop condition for many years to come. There really is no better thermometer on the market in my opinion, and as all my colleagues use the same one, it is also a professional endorsement.