Your issue is number of tests you get and the ability to accurately test FC. The HtH does not get it. I think it tests CYA like 4 times?
Or, you treat the pool as Seasonal - if it gets cloudy or other water issues, you dump it and start over. I would not suggest that looking at what it is taking to get to swim ready water.
Ok sounds like I better go with the TF-100. I agree dumping and refilling doesn't sound very good. It would end up the same the next time. I just have to figure out how to get this rust and iron out and should be ok.