I don't own any but I have a friend that does. He states is way easier for measurements and no more guessing. I would like phosphate, calcium, and alk.
I went ahead and checked out the Hanna Checker's page, although it was an exercise in redundancy for me, as I just picked up an alkalinity checker after researching them there.
I love the fact that the Hanna Checkers do the reading of colors for you. They are small, well packaged, and the checkers and reagants are affordably priced. I use my new alk checker daily, and my phosphate checker every 4-5 days!
I really like the precision and accuracy of the Hanna checkers. No other test kits on the market compare to these. I currently own the phosphate checker but I would love to own all the checkers.