Do you have plans to upgrade to a minimum 6 foot tank in the future, or are willing to rehome the fish within a year or two? If the answer is no to both, don't get a Hippo. 4' is way too small for an adult.
What people mean by 'ich magnet' is that if ich is present in a system, if your perameters are perfect and the fish is happy and healthy, it will be fine, but throw off a perameter or stress the fish and it will get ich. Odds are without quarantine, regardless of the stores QT practices, it is likely present in your tank, just hidden.
I got my own Hippo about six weeks ago. Lfs told me they coppered it, but after 3 weeks of observation, I forgot a water change, and next day, ich. Ich everywhere.