I purchased the SteriPEN shortly before going to Costa Rica for two weeks. The SteriPEN is light, packable and you dont need to buy expensive replacement filters (only 4 AA batteries!) Another plus is that there is no wait time like the salt brine unit from MSR.
I used it several times and did not get sick. That was water from a small stream in the rainforest. I encountered an older man who was pretty dehydrated so I used the SteriPEN to come up with some clean drinking water fast. The only thing you need to think about when using the SteriPEN, is that you need a container to collect water in, and then another to purify in, otherwise you have unpurified water on the rim.