Nano skimmers are not necessarily junk. They just dont have the bubble chamber size and dwell time to be as effective as larger in sump or external skimmers. Bigger, taller in sump or external skimmers will generally have longer dwell times for the bubbles to bounce around in the chamber and collect proteins on their surfaces. Nanos, not so much. The nanos reaction chambers are small so dwell time is at a minimal before the bubbles rise up into the collection cup. My experience with nanos was okay at best. i found they do provide some helpful added aeration to help with pH swings and a bit of a safety valve in the event there is some unexpected die off or nutrient spike. Like any skimmer, they can over foam if there is some sort of unforeseen die off or overfeeding, so in sump skimmers and nano skimmers that fit in an AIO chamber have some protections for foam spill off, but hang ons have the risk of dumping on the floor behind the tank. you can control nutrients with 10% weekly WC's but if you go the nano skimmer route it does have it's benefits. Draw backs for me were cleaning and frequency of cleanings compared to larger skimmers.