MisssMarie
Fish Addict
I hear mixed reports about adding them to your betta tanks. I hear they're good, but also degrade water quality, what's your opinion - should you add them or not?
IME bettas will act a lot more happier and will appear physically healthier when you put them in the tank, mine build bubble nests around them...... We'll I use oak leaves just because they are local to me but I highly suggest that you use Indian Almond Leaves instead of oak leaves 
Duckweed is a pain, it grows like wildfire.
You'd have to regularly thin it out
Not sure about it being a good aquarium plant, but I have water hyacinth in my pond.
It looks nice and is easy to take care of