ICP lab testing is a completely different method of testing and it is not really fair on the home test kits (digital and manual colorimetric assays) to compare them. Home test kits have limitations and interference that are different to those that affect an ICP machine. If they are not out of date and used correctly, home test kits still have value for testing Macro elements like Ca and Mg. They also provide an indication of Phosphate levels (even though they do not measure Total PO4) which is better than no measurement at all.
What Home test kits can't do is measure trace elements and, for this reason, it is not about having to choose between one or the other. Both forms of testing, when conducted correctly, have value in their own way alongside each other.
This is not a war between which is good and which is bad. It is like trying to argue which has more value, an axe or a knife?
You can read more information on the following R2R thread:
What an ICP-OES machine CANNOT test As the company that developed the method for sea water analysis and making broadband testing available to aquarists, we at TRITON often get asked what an ICP-OES machine CAN test. These days it is getting more and more confusing with the proliferation of...
www.reef2reef.com