This is an interesting discussion.
I have always wondered why people make a big deal about the weight of the SunRay. I swing an E-Trac (heavy machine) with a Sun-Ray probe and even when I have gone for several weeks without detecting I can still swing the machine for 8+ hours without feeling a thing. And I am not a man; I am a woman weighing at (as of this morning) 129 pounds and 5'7.... I do work out with light weights 3x a week and cardiovascular 5x a week. Although I weighed more a couple of years ago and was not in as great of shape, I still didn't have problem with the weight or balance. I'm 47 years old.
I think it is apples and oranges. Some people just simply prefer a handheld. I used one for two years before trying the Sun Ray and then never looked back. When I dig a 10 hole I would never be without the Sun Ray.
As for depth with a handheld, I think 1 is probably enough because it's really about pushing it around in the dirt you have excavated or else the dirt in the hole. With a Sun Ray, I use it to decide (as midas stated) whether what I am looking for is still in the hole, and if so, where. Given that, the 3-4 inches the Sun Ray gives is needed.
Just my two cents.