I have the Sievert with a primus bottle. When I first fire it up it is great but by the time I move it across to the fitting it is like a glorified lighter! It still does the fittings ok and have never had a leak with it yet but it is infuriatingly slow at times. I have had it stripped down several times but it makes no difference. The only time it has worked as it should was when I took it back to where I got it from. The guy there switched it on and then was able to move it around for a couple of minutes all the while with a full power flame. I took it back and the first time I tried to use it on a job it just went back to the low flame.
I would sling it but at the price of replacing it and the fact that it still works means that I will just hang on to it.
I had the sure fire one previously but after a couple of days I accidentally bumped against it and it broke in two!