I've only had it a few weeks but seems to work like a charm. I've had no problems at altitude but my highest altitude so far has only been 10,000. It seems to work well on very clear water too. I've had none of the issue that others reported with that.
I like the size and ease of use. Plus it's nice to get a bottle of ready in just a few moments when you're thirsty!
This review was written in the old system and had content requirements that are different than reviews written today.