The "II" Tesoros (no matter which model) were/are a good bit quieter in heavy trash (especially iron) than the uMaxes that came after them. Like our Tesoro guru Monte, I have seen this first-hand with the Silver Sabre II vs. Silver uMax and the Bandido II vs. the Bandido uMax.
Plus, the Silver Sabre II is IMO far more versatile than the Silver uMax by virtue of the "Reset" toggle (which the Silver uMax doesn't have) because I've found ways to have that setting reject stuff like pull tabs.
The other major difference is the current uMaxes is their "signal boost" circuitry that gives you the artificial *impression* that you're detecting deeper, but you're not really detecting deeper by virtue of more raw power. Yes, you'll *hear* smaller stuff deeper (maybe), but you'll also hear a ton more trash and get more snap-crackle-pop especially in small iron -- and often in places where you really don't want to need to hear that sort of stuff.
IMO, anyone would be a good deal better off with the "II" Tesoros than the current-generation uMaxes.
Scott