I learned how to MD by borrowing a friend's 250, which was very easy to use. When it came time to buy a detector, I thought "well if the 250 is good, then the 350 must be better". Not quite. Don't get me wrong, the 350 is just as easy to use and the DD coil finds some really deep stuff (even though the depth display only goes to 8 inches, my 350 regularly picks up targets well over 12 inches deep in certain soil). However, my depth indicator is nowhere close to being accurate. Pass a penny an inch under the coil and it will show up as a dime at 6 inches. In coin mode, the 350 finds more bottlecaps than coins. When I'm coin shooting, I find the all-metals mode works best... but then you're limited to hunting out-of-the-way places where there's less junk. The built-in pinpointer is less than worthless.
But there is one really good thing about the 350. The batteries seem to last forever, unlike all the 250s I've used, which all seem to eat batteries like candy. The bottom line is that if I had to choose all over again, I would've gone with the 250 and saved myself a few bucks.