I wouldn't know how to answer your question well, but just to throw in a bit, I use a pinpointer, when a situation calls for it. I have the Sun Ray probe on a couple machines, but for the machines that don't, I have 7 pinpointers. Two are of the same model, so really 6 models. I found a working unit while out detecting, so someone out there lost one. I find all work to one degree or another so personal preference for the type of hunting is a factor. There are other units to consider, and if you have a local dealer that has a variety, or a local club, then options can be available to actually test the unit's.
Anyway, instead of covering them all, I'll give a little on a few portable pinpointers. I believe the Vibra-Probe offers a newer unit now.
Pocket Uni-Probe: This unit has depth. Cost, but the depth is very good. Audio with adjustable frequency and threshold.
Vibra-Probe 560: Waterproof with automatic on/off by tilting the unit up. Target needs to be close to tip to signal/vibrate. Durable.
Treasure Mate: Sensitive at the tip. Adjustable Ground Balance and Tune knobs. Tone or vibrate with target close to tip.
Just to show somewhat of a size comparison:
[attachment 77034 Pinpointers.JPG]