There are several characteristics that define a good strength training machine:

1. Adjustability: A good strength training machine should be adjustable to accommodate different body sizes and exercise ranges of motion. This allows users to perform exercises with proper form and to target specific muscle groups effectively.

2. Durability: The machine should be built with high-quality materials that can withstand the weight and pressure of heavy lifting. This ensures that the machine can last a long time and can be used safely and reliably.

3. Safety Features: A good strength training machine should have safety features that protect the user from injury, such as safety locks, adjustable safety stops, and ergonomic grips.

4. Smooth Operation: The machine should provide a smooth and consistent movement throughout the exercise range of motion. This allows the user to perform exercises with maximum effectiveness and reduces the risk of injury.

5. Versatility: A good strength training machine should offer a variety of exercises that target different muscle groups. This allows users to perform a full-body workout and target specific areas of the body that they want to improve.

6. User-Friendliness: The machine should be easy to use and understand, with clear instructions and intuitive controls. This allows users to focus on their workout without worrying about how to operate the machine.

7. Comfort: The machine should have comfortable padding and grips to reduce discomfort and prevent injuries. This encourages users to stay motivated and continue using the machine.