I use a non-contact all the time. I also use a Vol-con for checking continuity and grounds, and an Amprobe ACD-10 clamp-around DMM when I need accurate voltage and current readings.
The non-contact is nice because it fits in your tool belt or pocket, but its not very rugged.
The Vol-con is almost indestructible, as I've thrown it, dropped it and abused it and it still works.
Of course, always "test your tester" first, especially the non-contact.
So, I would say all 3 tester types are essential to have.
