I used the SteriPEN Adventure Opti for several trips 2 years ago and it worked well. I had issues with a friends identical pen the previous year, yet. I was able to eliminate those issues by drying off the tube after each use. We had issues when we had tried to use it for several liters at a time.
Last year, I like the idea of the Sawyer 3-way inline water filter and decided to give it a go. It only weighs 3 oz, no bags, no extra batteries, and it will gravity feed as well. I always carry a bladder so it worked out well. I too bought the SteriPEN as I thought this would speed up my water gathering time, yet, I found it really wasn't that much faster than just getting out my bladder, filling, and walking again.
Because I understand any filtering device can fail, I always take drops as a backup. This being said, I personally feel there is a greater chance for the electronic device to fail than a filter, and given the filter weighs less than half the pen, I sold the pen.
I think you will enjoy the pen if you get one and it works for you. It does seem the reviews are better now than in the early days. I also found using a 1L platy with the top cut off worked real well with the pen. It rolls up into nothing so you can store it close to the pen for easy access and the side mouth makes using the pen real easy. Maybe it was a personal thing for me, yet sitting there and twirling that pen for several liters, just wasn't that enjoyable.