Well, to start off with, The Quality of the XT70 is not as good as the Quattro, the depth of the 70 isn't close to the Quattro in my soil. The Target ID isn't quite as solid on the XT70 as it is on the Quattro, but your talking a single frequency versus 28 frequencies of the Quattro.
Now just speaking on the Quattro, it's a great beach & relic machine and even a decent coin machine. In my soil, it will hit targets at 12+ inches with no problem. I love the graphic pinpoint feature of the machine, But, it's a heavy beast at close to 5 pounds with batteries and stock DD coil. It's about worthless in trashy areas or parks & ballfields and such due to having a Vvvvvvery slow target recovery speed. You actually have to stop swinging and allow the processor to reset itself after each target if not then you WILL miss targets completely. Also the tones take a little getting used to.
Now, the Xterra 70 is very light at less then 2.9 pounds, it's great at the beach the same as the Quattro, but probably 2 pounds lighter for all day swingin. To me the ID isn't quite as accurate as the Quattro and the depth aint even close to the Quattro. I would put the depth at about equal to the CZ5's, CZ3d's, Cortes & Garrett GT&i's. Plus the 70 has a super fast target processor so you can swing it fast or slow and not miss any targets. I used my 70 at a comp hunt last month and it worked great. But there were 3 or 4 guys using Quattro's at the comp hunt and they were gettin pretty frustrated with them and the slow recovery time.
Now when I say the Quality isn't as good as the Quattro, it's not a put down on the XT70, BUT I think they had to sacrafice a certain amount of solid construction in order to make it light. The construction on the Quattro is great, built like a tank, but weighs like it as well.