Question: 
Can you give it percentage to open commands or set custom stop points? Or its just completly open or closed?
Answer: 
You can setup custom stop points. i only open mine halfway.

Question: 
If i have two curtain panels, do i need to buy one product or two? i can't figure out for the description how many devices come in a pack. 
Answer: 

Just one device comes per pack, if you have two panels and they open in opposite directions, you would need two switchbots.

Question: 
What is the item weight?
Answer:

It weighs nearly 500g.

Question: 
What is the difference between the I and the U model?
Answer: 
It's the type of rail your curtains are ,urail the slides are inside the rail ,irail the slides are outside of rail.