Any coil will get gunked up and look like crud. With that being said it will depend on the
juice you're using as to how long it will take to get gunked up. Replacement heads for the protank are cheap and can be rebuilt. Replacement heads for the iclear 30 probably aren't to expensive either. Both can be cleaned and used again, and both will loose flavor as the coils get gunk built up on them, indicating its time to clean, replace or rebuild the coil/head unit.
Typically the darker the
juice the quicker it will gunk up a coil and the clearer the
juice the longer the coil will stay clean. Some clear juices have sweeteners in them which will cause a coil to gunk up fast as well due to the sugars caramelizing. With proper cleaning techniques I have had coils last for many many months but they do still loose their performance over time.