I have the BH Junior and the BH Tracker IV.
The Tracker IV is actually a really nice machine for the money. I picked mine up for $89 on Ebay a couple of years ago. Depth is decent and it is lightweight which is good for a 9 year old. My 9 and 11 year olds have both used it successfully. I also like the fact that it is a two tone machine as opposed to just one tone. That really helps when trying to figure out what is under the ground. I actually use this feature to sort pennies when coin roll hunting. Zinc pennies give a low tone and copper pennies give a high tone when the discrimination is set all the way up. So that's a nice bonus for me.
I would pass on the BH Junior though. It was cheap and it worked fine for my son when he was 7. But it is not a deep detector and the handle is not conducive to swinging the detector properly. The way the handle is made makes kids want to swing it in a big arc. It also doesn't have a headphone jack so it makes a lot of noise out in the field which attracts the attention of the other kids in the area.
I don't have any experience with any other BH detectors. But I can also readily recommend a Tesoro Silver uMax if you are interested in a deeper machine that is lightweight and easy to use. But it goes for a little more than the Tracker IV.
Good luck.
