One thing beginning vermicomposters should be aware of is ants, especially in the spring. To combat this, you may need to place the legs of the bin in a water-filled baking tray or individual cups of water. The water creates a mote-like barrier that prevents ants from accessing the food in your worm bin.
You're a bit limited in expanding the size of your bin. The design will provide the average apartment dweller with plenty of composting power. But you can't just add a 3rd, 4th, or 5th tray. The tiny legs would likely buckle under additional weight beyond the provided trays.
Finally, the last issue is that worms can get stuck in the base tray with the leachate. You can line the bottom and try to prevent this, but the worms will likely compost the lining. Be sure to drain your leachate frequently, preventing worms from getting stuck and drowning.
These are honestly minor issues. If you are looking for a small stylish worm composter, this is one of my favorite designs. Be mindful of pests in the spring, and you will be well on your way to composting success.