Better penetration in mineralised ground and smoother operation are the biggest advantages of the pulse induction (PI) Minelabs. Generally as you go up through the models they have released their performance and ease of operation improves. The GPX series has fantastic sensitivity to small Gold. Much of what I have found is only 1-2 inches deep so it doesnt mean you are always digging large deep holes. The coil that is used also makes a difference. Generally speaking larger coils are best for larger and deeper targets. Smaller coils can be worked close to the ground and often find small bits larger coils miss.