The D is for people who are afraid their employees will break the knob on the HT version. If you do, you just have to remember that the board is in there so you don't ultrasonic it for 40 minutes. I don't think it is worth the extra money for the simple reason that you have to hit a select button to change from time/temperature/UC strength rather than immediately adjust dials, and you also have to wait 2 seconds when you turn it on for it to come on. It's very 1980s alarm clock, and a pain in the ass.
We sell them all now. We became a distributor of Crest: you can buy here.
We sell them all now. We became a distributor of Crest: you can buy here.