I don't have the Bullseye, but I've heard ALOT about their switch problems...
So got the Vibraprobe 570 a couple weeks ago, and I LOVE it!!!!
The thing is definitely alot longer than I imagined, but it works flawlessly!!
I really like how it vibrates more consistently as it gets closer to the target.
As far as depth, I haven't noticed. But it's worked for me every time I've been out and helped me locate my targets quicker!
I have noticed that my detector (White's IDX Pro) sets it off if it's close to it and I start detecting before the 570 turns off... but so far that's not a huge deal for me at all. I'm going to try to make a velcro strap for it so I can attach it to my backpack strap on my chest, so it's out of the way.
Bran <><