I've never carried a full on filter. I've hiked with guys who do and my opinion was always that they were bulky, time consuming, and just not 'hiking' gear.

That's why I picked up the MIOX Pen. I guess had the Steripen been readily available when I made the purchase I could have gone either way but I'm not unhappy with mine in the least. My only beef with the steripen is that the water needs to be clear and you need to have the right bottle to get it inside. I like narrow neck bottles and bladders...seems to me like the Steripen would be awkward with those vessels.

I also carry MP-1s as backup.