The underlying Tesoro technology is not as "ancient" as some apparently think. VLF technology reached its peak decades ago; that's why some 25-year old machines are just as deep as any modern machine--they use exactly the same "outdated" technology. (Even Minelab's latest multi-Q machines, which I like, are just the latest wrinkle on VLF technology.) Tesoro even did a fairly good job miniaturizing the circuitry at the time, producing light machines. Where it fell short was in failing to continue the process of evolution--squeezing out a few more drops of performance, evolving the packaging, the controls, and the way information is presented, etc.
I happen to like the straightforward analog approach at times (I have both types of detectors), with reliance on knobs and tones, where you don't need to use switches to sort through endless menus and options. But, Tesoro should have firmly embraced multi-tones long ago (rather than just making a few abortive stabs), should have a few models with large, bright TID screens, as well, since that's what the market wants. It should have introduced other modern features like, sleek, waterproof/resistant designs, li-ion batteries, wireless headphones, etc. Mostly "bells and whistles," built on the same underlying "ancient" VLF technology; but, that's what sells.
The Tesoro brand is definitely worth something. The Tesoro technology is, as well, since you could easily modify some of the circuit designs to be the basis for some sleek, modern machines. Of course, most of the basic VLF technology is probably firmly in the public domain by now.