So im looking to purchase a multi meter such a the nutri dip meter. But the nutri dip meter is almost $200. Anyways i started looking and found knock offs that are half that price. Like http://www.ebay.com/itm/6-in-1-Digi...ity-Tester-EC-CF-TDS-ppm-PH-C-F-/181214132593 . Has anyone ever tried one of these?