I have one of the older steri-pens (classic) that uses AA batteries.  It works very well, but I also use micro-pur quite a bit.  Much easier than iodine and not as much of a bad taste.  But the bottom line is that the steripen is very good for smaller quantities of water.  I always bring along micro-pur as a backup, and prefer bleach for larger quantites of water in camp.