Kodak makes better thermometers that are not too expensive. So does Jobo. Of course, you can buy them even cheaper used on eBay.(posted 8691 days ago)If you get a cheap digital, make sure you check it at the temps you are running. People seem to believe that since they read out to a tenth of a degree, they are accurate to that, NOT. You have to get up to the couple hundred dollar range to get accuracy in the degree range.
With Xtol at least (I just did some HP5+ in Xtol so I have the info handy) there is a significant difference in time from 70 to 72 degrees, so accuracy is fairly important.
One thing to watch with any wet (alcohol or mercury) thermometer, is that in shipping you may get separation in the liquid column. To fix, get a pan of very hot water, and carefully dip the bulb in and out to raise the column to the top. This will reconnect the liquid column.
I ran into this this weekend. Things didn't seem right, so I checked my one thermometer against my Kodak Process Thermometer (VERY accurate) and found a separated liquid column. A little hot water and it reads within about 1/2 degree of the process thermometer.