I wrote a review for the 30oz version as well. Basically, this cap (when the bottle is filled) is extremely difficult to unscrew. I believe it is not just child-proof, it is person-proof. No one wants to end a long day of hiking by wrestling with the fuel bottle so they can start dinner. Ugh. I'm so glad I have an older bottle. Hopefully they fix this cap before I need a new one!
This bottle has worked out great. I was a bit concerned about the small size at first, but it holds plenty of fuel to cook for a couple of meals over a few days of camping, which is just what I need. And it's the perfect size to fit into my MSR stove's stuff sack.
I bought the smallest fuel bottle to carry along with my Svea 123 camp stove. The bottle provides about two refills.