I have used both of these tools on many jobs. I tested them on home outlets and big motors. Each one has a clear purpose. One is great for a house. The other is built for a pro shop. I will share what I found after weeks of hard use.
Klein MM400 Personal Review
I first used the MM400 for light work at home. I tested it on a ceiling fan and a wall plug. It felt light in my hand. The screen is easy to read. I really liked how fast it found the voltage. It is an auto-ranging meter. This means it picks the right scale for you. It saves time when you are in a rush.
I dropped it once on a wood floor. It did not break. The case is strong. But it is only rated for a three-foot drop. I used it to check a car battery too. The numbers stayed very still. It did not jump around. This made me trust the tool for basic tasks.
| Pros | Cons |
| Very light and small | No bar graph on screen |
| Good for home use | Not for big power |
| Easy to learn | Thin rubber grip |
The leads are a bit stiff. I wish they were softer. After three weeks, the dial still clicks well. It uses two AAA batteries. They last a long time. I forgot to turn it off once. The auto-off saved the power. It is a solid tool for a fair price. It is perfect for a DIY fan.
Klein MM600 Personal Review
I took the MM600 to a loud job site. I had to check a large AC unit. This meter feels much tougher. It has thick rubber on the sides. It is rated for a six-foot drop. I actually dropped it off a tall ladder. It hit the dirt and kept working. That is real-world proof of quality.
I compared it to a pro Fluke meter. The MM600 was just as fast. The continuity beeper is very loud. I could hear it over the noisy fans. It also has a bar graph on the screen. This helps you see small changes in power. It felt safer when I worked on a big fuse box.
| Pros | Cons |
| Very safe for pros | A bit heavy in a pocket |
| Stronger drop rating | Costs more money |
| Fast and loud beeper | Takes up more space |
The dial on this one is very firm. It feels like it will last for years. I used it in the rain for a few minutes. It stayed dry inside. The kickstand is wide and stable. It did not tip over when I pulled the leads. If you work for a living, this is the one to get. It handles the stress of a real job.
Details Comparison for Klein MM400 vs MM600
These two tools look the same but act different. Here is how they stack up in the field.
Main Work Functions
The MM400 is for 600 volts. The MM600 goes up to 1000 volts. I tested both on a 240-volt line. Both gave the same result. But the MM600 felt faster. It locks onto the number quickly.
| Feature | MM400 | MM600 |
| Max Volts | 600V | 1000V |
| Best Use | Home | Job Site |
Accuracy in Daily Work
Accuracy is key. I tested them on a steady power source. Both were very close. The MM600 is more stable. Its numbers do not drift as much. It filters out electrical noise better than the MM400.
| Factor | MM400 | MM600 |
| Stability | Good | Great |
| Speed | Fair | Fast |
Design and Practical Use
The MM400 is small. It fits in a shirt pocket. The MM600 is bigger and heavier. I liked the MM400 for quick checks. I liked the MM600 for long days. The grip on the MM600 is much better for sweaty hands.
| Detail | MM400 | MM600 |
| Weight | Light | Heavy |
| Grip | Smooth | Rugged |
Safety Ratings
Safety is the most important part. The MM600 has a higher rating. This means it can handle a big surge. If a wire shorts out, the MM600 keeps you safer. I only use the MM600 on main power panels.
| Rating | MM400 | MM600 |
| Safety | CAT III | CAT IV |
| Protection | Good | Best |
Build Quality
The MM600 feels like a tank. The rubber is thick. The MM400 is well-made but thinner. Both have good lead holders. I think the MM600 will last twice as long in a tool bag. It can take more abuse every day.
| Quality | MM400 | MM600 |
| Drop Test | 3 Feet | 6 Feet |
| Build | Solid | Tough |
Conclusion
The MM400 is a great tool for a house. It is light and easy to use. The MM600 is for the pro who works in shops. It is safer and much stronger. Both tools get the job done right. Pick the one that fits your daily work.