Terry,
I own at least one of the following detectors; a GMT, a GB2, a GBSE, A Lob ST, a TDI and a TDI SL and have used them all. With that said I have used all of them in AZ but the TDI SL and I have used all, including the SL all in various types of ground here in CO, matching the ground found in AZ. So, with that said I know you are simply wrong with your statement about the TDI. In fact, I field tested the GB 2 and the LST and several other gold machines for Lost Treasure with most hunting done across AZ. So, yes for those wondering, I have hunted from Gold Basin to Tucson, from the Bradshaws through the Weaver mountains to other areas not known by many. I hunted the La Paz area before it was closed off and of course around Rich Hill, Wickenburg, Salome, East and north of of Phoenix, LSD, Model Creek, Quartzite, and a whole lot of other locations across AZ.
Now, people are certainly welcome to follow you and our advice and I hope they do such as trying the Tesoro's PI's for gold hunting. If they do, I really hope they are willing to come forward with what they found, especially if they can compare Tesoro's PI to the TDI.
BTW, I tried one of Tesoro's PI's years ago and found it didn't work well in bad ground.
None of the VLF's mentioned nor can a non ground balancing PI match the TDI in bad ground for depth or ease of use. So, either you didn't use the TDI as much as you said, or you simply don't know how to use it. I am not sure just which one is correct.
Reg