Ivan, I've owned a 250 for a few years, and a 350 for a little over a month. Don't misunderstand what I'm about to say, I'm not unhappy with either. It's my belief the 250 is a great detector which is well worth its price, all things considered. It's inexpensive, and is a coin magnet for the most part (except nickles).....it's also an aluminum magnet, most of which rings-up as a coin. When the 350 was announced, it was over-hyped as some miracle. It's not, but don't take that as it's not a good detector. It's just a 250 with a larger coil (basically). My 250 & 350 air test the same, and swapping coils (something Garrett claimed "worked") cut depth (air testing) by over 1/3, and caused chatter on one, until sensitivity was lowered. Only reason I'm saying all this is, just because a manufacturer releases a new model, doesn't mean it's any better than the previous. I bought the 350 strictly as a back-up, and had been considering a larger coil for the 250 anyway, so I had little in the way of expectations from it being much different than my 250. If I had, I'd have been a bit disappointed. But I guess that's how advertising/marketing works these days.
I can't speak on Tesoro, because I've yet to have my hands on one, but over the past few years I've been involved in the hobby, I've heard nothing but good about them, and yes, their warranty speaks loads about them (IMO). I've gotten to the point where I feel this hobby is something I'll be involved in for as long as I'm able physically, so it was time to invest in upgrading detectors. I'm not knowledgeable about the inner-workings (electronics) of any of these machines, so I don't have a clue as to what makes them better, or what could be done to improve any of them. Perhaps Tesoro was ahead of their time, and got it "right" early on, and every one else has been playing catch-up? I mean, if they have something that works.....why change it? If they (Tesoro) just put the same stuff in a new housing (or just stuck a new coil on the end), and released it with a lot of advertising hype, I think that would do more harm than good. That's one (the main) reason I'd chose this time to try another brand.....Tesoro. I think another brand is going to lose a few customers, only time will tell.....
Smitty