Carl is right about the dowsing. I would stay with a good PI if the choice were mine.
Now, with that said, looking for an alternative for the ML is something that many people try to do. People have looked at the other PI's you mentioned but I can't comment on them since I haven't tried them. So I will leave any discussion about them to others.
Your final comment about what is a prospector to do indicates you are wanting a PI to look for gold nuggets. With that in mind, I will confine my statements to that arena.
If you are looking for gold nuggets and hunting in the US, then most of the gold you will find will be smaller, like less than 1 oz. Actually, most gold found is much less than 1/4 oz.
To find such gold, you need a detector that has a relatively short delay. The smaller the gold you want to find, the shorter the delay has to be. So, lets say you want to find gold in the gram range and larger. Now, this will require you have a detector that has a delay less than 15 usec or so to get any type of decent response on the smaller stuff.
If you want to find nuggets down in the grain range, say 3 to 5 grain range, then you really should have a PI that has a minimum delay of 12 usec or even less. A lot depends upon other circuitry, overall sensitivity of the detector, etc.
There is a down side to reducing the delay. The shorter the delay, the more ground signal you will encounter. So, selecting a different PI will require careful hunting techniques, especially in some areas.
Other areas, there will be little or no ground signal to contend with, but such areas are not that common.
ML has ground balance built in so one can be quite sloppy with their sweep techniques and still be successful.
Since most other PI's do not have the ground balance feature, then one has to be much more careful on how they do move the coil. Increasing the SAT control, which is a form of autotune helps a lot.
Another great help that is not yet readily available is the use of a DD coil. This will greatly reduce the ground signal and helps in other ways. For example, surface iron objects will have a tendency to give a reverse signal, or stated a little differently, a wide double blip which makes distinguishing this type of trash much easier. Deeper iron objects will, unfortunately also generate a positive response.
There are some who really like the new Garrett Infinnium which also has some form of ground balance. I haven't tried one so I will not dwell too much on it, except to say that the biggest complaints I have heard is this detector doesn't find the really small gold (in the few grain range) and the selection of coils is not that great.
Eric's detectors, such as the Goldquest (GQ) will do quite well in the detection of nuggets down to a few grains in size. However, there is no ground balance feature so one will have to be more careful with their sweep techniques to minimize the ground signals.
The GQ is a considerably less expensive alternative, is lighter, and very reliable. But again, one cannot expect to buy one and then try to compare it directly to a detector that costs 4+ times as much.
Also, the GQ is ground sensitive which means the ground will produce a response. Increasing the SAT will help but will not eliminate the problem. Again, the best solution is to search slowly and try to maintain the coil at a level height above the ground. In the really bad areas, one should probably raise the coil a little higher off the ground when searching to minimize the ground signals.
I hope this helps explain what you are up against in your search for a detector.
Reg
