I've tested several brand GPX mono coils on the bench (using several test instruments) and compared results against similar shape and size coils by ML. The only performance advantage I see going from ML to aftermarket coils is the gain one might get going to flat wound as opposed to a bundle wound, plus aftermarket maybe a bit beefier... more durable.
I test ~8 different parameters. Some coils test horrible, some very good when compared to ML but nothing so far has tested better.
My detecting buddy gave me a few coil types I didn't have so my test database grew & made more sense. It was no surprise what his favorite coil was after testing all his coils. I told him what coil of his gave the best result, his reply was... that coils his favorite!
My advice;
- choose a coil for a purpose, not what its proclaimed to do
- choose a quality constructed coil
- choose a quality manufacture who supports their coils
- choose a coil thats proven in the field
- choose a coil for a purpose, not what its proclaimed to do
Lastly, choose a coil for a purpose, not what its proclaimed to do!