Normally, you don't need anything special to hear targets. In the normal ID motion
mode, all targets basically are the same appx volume, so a weak target will be
about as loud as a strong one. There might be a bit of advantage in the PP mode,
but nothing too great. The signal will pretty much be there, or it won't.
So really, all it boils down to is being able the hear the normal sounds you are
hearing now. Hearing varies among people too. My hearing is pretty good, so
I don't need a lot of volume. I use a single mono earphone. But not as a ear phone,
as the actual speaker on the machine! I can hear everything just fine with it clipped
to my arm band. I've never had to stick it in my ear.
The stock 250 speaker is ultra loud for my tastes.. I had to throttle the volume way down,
as it was way too loud for me. But I also get the benefit of lower battery consumption.
I can hear it fine, but not many others can. Heck, I hear the constant jet turbine
whine on mine.. Like I said, I'm not hard of hearing yet.
I don't like to wear headphones in general when detecting. Get hot, muffle
surrounding sounds, etc..
BTW, if you use phones on a 250, they must have a volume control.
I'm sure someone mentioned it in all the posts.. You'll blast your ears
with it straight. I don't think there is much resistance added to the phone
output, vs the speaker leads.