If you want to open and close according to light level or time, or a combination of these then the chickenguard ASTI Premium door opener is the door opener you'll want. This unit will lift up to 2kg.
If you live somewhere that is either hot or cold then the chickenguard ASTx Extreme door opener is the one to choose. This has uprated components and weather proofing to give it an operating range of -30c to +50c. It also has the strongest motor lifting up to 4 kg.