I got an intank too. After using for several weeks I began to have concerns. Water takes the path of least resistance. With the intank system it fundementally breaks this rule. The water over flows into the "intank" but water hits the water there and no longer has the force to penatrate lower levels. If you use purigen, you will see that it never turns brown. I left mine in for 7 months. Never changed color. Thus indicating it is not getting hit with as much tank water as it should.
So to test my theory, put "intank" in a clear container with sink water running through it. Then add food coloring. The water never makes it to the bottom. Just my 2 cents.