In my opinion, it really comes down to what you intend to feed. I’ve had both, the eheim is a decent feeder, but I prefer the plank for a couple of reasons.
The Eheim feeder revolves and has an opening to allow the food to drop into the tank each time the port makes a full turn. If you are using flake food, or freeze dried and the feeder drops it that type of food just floats since it hasn’t been hydrated. If you prefer using a mixture of pellets, flakes and freeze dried, all having different sizes, that will cause a different issue. To accommodate the larger sized flakes or freeze dried you will need to slide open the feeding port to allow the larger food to get through, which will end up dropping a ton of smaller food, more than you probably want to drop in.
I also found that this feeder was a bit unreliable regarding uniform amounts of food being dropped into the tank at each feeding. It works best if you choose to fill it with one type of food only.
The way the plank works makes it much more versatile. The food is pushed out with an auger, so all sizes of food can be simultaneously fed at each feeding. It also has a long tube with a small sicce pump that mixes that food in the water to hydrate the flake and freeze dried and it then released from the bottom of the tube and out into the display tank without just floating into the overflow. This, allows you to feed all types of food of different sizes, textures, and even freeze dried mixed together.
I prefer having a mix of many different foods to feed the various sizes and feedings habits of my different fish. So, for me, The Plank was well worth the money.
