Most anything is better than nothing. Guaranteed, the blade will find it.
There are extensive threads discussing this very question in the past. Some of the members have hand held machines that cost thousands of dollars. Some members have hand held machines that are in the hundreds of dollars. Most of them say that their machines do a pretty good job. You just have to developer a technique for your machine and your operation as well.
I'm not aware of any members who own a "tunnel" detector, that takes whole logs,as you might find in a big commercial mill.
Put "metal detector" in the forum search (access at top of the page) and you will find pages of posts.