I have never personally used those test strips, but I have been told by several trusted 'fish people' (including some that tested using the strips and 'usual' tests)...the strips tend to not give reliable results.
My personal experience with those is limited, as mentioned, but negative. I had tested my tank's water, then that same water (same container) was tested at 1 of those major chain pet stores using the strips.... My results were much more accurate. The strips actually didn't read anything for ammonia/nitrite...and had my pH wrong too. That same water was also tested at another store using the 'usual' tests w/ the same results I'd had at home.
But I also know some people like them, so it's another thing to add to the personal opinion and experience list! :)