Drops are cool, if you only need to test one bucket. Would hate to see someone trying that method on 20 plus buckets. Lol
My cheap $20 pen and $10 of calibration solution (and I had to buy a $2 battery also) have lasted me almost 5 years now, still plenty of life left in both the pen and solution. Could not even imagine how much that would have cost me in drops this far. Plus all the man hour savings durring all those years and all those buckets.
Really depends on what you are trying to do with it that makes it worth it or not.