Yes the IDX is a very good detector once you understand it's functions as WV-Detecting pointed out. I have a modified IDX Pro and bought a Classic ID which is basically the classic IDX without the Black Sand switch. I was a bit disappointed with depth on the Classic ID especially when using smaller coils and found i couldn't make the detector go bonkers at full sensitivity and sent it out for the mods and Whamo it was every bit as good on depth as the Modded IDX Pro.
The Classic IDX is excellent at target separation especially with a smaller coil and the All Metal ID is a high value facet on this detector.
Your Dad has a fine detector but with the modifications available on this unit it would become an outstanding detector in my opinion and worth the money if he likes the IDX. HH Bill