To break it down, your choice of combo kit should be determined by the following factors:
1. How often you will use the power tools (daily or occasional use).
2. Will you be transporting your power tools or using them in one location.
3. What type of work will you use your power tools for, specifically which power tools do you need.

Typically, features to compare include:
1. Power voltage and battery type: Power is one of the biggest variables when it comes to cordless power tools. Batteries are typically available in NiCad or Lithium Ion and run from 3 to 36volts of power. You usage should determine how many volts of power you need in your cordless combo kit. Will you be using your power tools for several hours each day or will you be using them for occasional projects around the house. The higher the voltage, the more power you will get from your cordless tool.
2. Variable speed motor: adjustable motors are an advantage when working with varying material density types.
3. Easy or keyless blade change: look for tools with a keyless chuck or easy blade change for safety and convenience.
4. Positive miter and bevel stops: this makes cutting accurate miter joints and bevels easier.
5. Adjustable handle: some cordless power tools have adjustable handles which makes them more flexible for tight spots, angles and overhead use.
6. Electric brake for safety: this is an automatic stop included on saws that makes the saw stop spinning when you shut off the motor.
7. Dust port: makes it easy to connect your tool to a dust collector or shop vac.
8. LED lights: light up the work area as you press on the power switch. This feature is nice for when you are working in cabinets, closets or anywhere where the light is at your back.
9. Durable magnesium housing: magnesium housings are lightweight as well as strong and durable.
Cordless combo kits are a great way to get all the tools you want and need with one purchase.