I use a classic Steripen, and I too had some issues getting it to work reliably. The button is supposed to be pushed with the contacts OUT of the water. The unit blinks green slowly, and the operator has some time (~15 sec?) to immerse the lamp and contacts. When the contacts are immersed, the lamp lights and the water is disinfected. I had been pushing the button and holding it down and kept getting errors (flashing red.) I discovered that only a very brief push of the button is required for the unit to work properly. I have also noted the presence of the drops of mercury in the inner light tube, and I sometimes shake the unit before activating it to make sure the mercury is distributed through the tube. I have never been at all concerned about mercury poisoning since the tube is hermetically sealed, and is inside a second tube. The tube is essentially a fluorescent light tube made of quartz and without the phosphors to generate visible light. The mercury is essential for the generation of the UV spectrum. I would not be concerned about the mercury at all, unless, of course, the tube gets broken.
I use disposable Li batteries, and I have found that the unit is more finicky in colder conditions. I also carry chlorine dioxide tablets as a backup.
IMHO, I like the Steripen.