I can help a little even though I've never used the earlier C. The early ones are more the "lunchbox" style and therefore would be somewhat heavier. You may be able to pull up the manual on the Tesoro factory site and see the manual.
The umax model is nearly the same as the Silver Sabre umax with the following differences. A 3 way frequency switch, an all metal/disc switch with VCO all metal tone.(SSumx has momentary pinpoint button for all metal) I have both and the performance is pretty much identical. The earliest umax models had the frequency switch on the back of the box, the later have it on the faceplate. The earlier ones came with the 8" donut coil, the later the 9X8 spider. Don't know for sure whether the earlier umax had the VCO, but the more recent one I have does. Preset ground balance and a somewhat lower pitched tone than the SSumax. I've had very good success with mine using he 7" concentric coil in parks etc. and it's a great combination for planted coin club hunts. Hope this is helpful.
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