I've used the tube for 2-3 years now and love it for cold smoking. I only light one end (with a kitchen butane torch) and blow it out after about a minute of flame. Put it in the bottom of my smoker with the lit end slightly elevated. Produces a lot of smoke and burns very clean - very little ash afterward that I just tap and shake out.
I've used it for cold smoking steaks, cheese, and home-cured bacon. I can get 4 hours when filled, but I usually just half fill it to get a couple of hours smoke.
I don't find the smoke harsh at all - gives a good flavor, especially with cheese.
My grill only goes down to 180, so the tube is my only option for cold smoking (I don't use the tube when hot smoking - I get enough smoke from my grill for that.)