Hi, did someone of you use one of those cheapo EC testers from ebay and can tell me if they do their Job or if they just totally suck? something like this: http://www.ebay.com/itm/LCD-EC-138-0-6-inch-Accurate-Mini-Pen-Type-Electric-conductivity-Tester-Blue-New-/400570310235?pt=LH_DefaultDomain_0&hash=item5d43d9de5b