Okay, let's break down your assessment of this multimeter. It sounds like you're pretty disappointed with its performance, and your points are well-articulated. Here's a summary and expansion on your concerns

Key Issues & Concerns:
Slow Refresh Rate

This is a major drawback. A slow refresh rate makes it difficult to capture rapidly changing readings or to troubleshoot dynamic circuits. It also makes finding the right reading take longer.

Low Input Impedance (0.8 MΩ)

This is a significant issue, especially compared to the standard 10 MΩ for general-purpose multimeters.

Loading Effect

Lower input impedance can significantly load the circuit you're measuring, affecting the actual voltage reading, especially in high-impedance circuits. Think of it like a pressure gauge that leaks air; it lowers the pressure it's trying to measure.

Not Lo-Z

You're right, 0.8 MΩ isn't truly "Lo-Z" (Low Impedance) mode, which is generally much lower (typically <10 kΩ or even lower). Lo-Z modes are designed to eliminate ghost voltages caused by capacitive coupling. But your multimeter impedance IS low enough to make a difference, just usually not for the better.

AC Mode DC Voltage Issue

This is a serious defect and a red flag. The AC voltage range should only be responsive to AC signals.

Amplification Effect

The fact that it reads double the DC voltage in AC mode with one polarity is bizarre and indicates a fundamental flaw in the AC measurement circuitry. It suggests that the multimeter can't block out DC signals, and it amplifies the DC signal instead, which leads to inaccurate measurements.

Polarity Dependence

The behavior changing with polarity reinforces the idea of faulty rectification or filtering within the AC measurement section.

Overall Performance vs. Cost/Certification

The fact that it performs similarly to a basic Harbor Freight multimeter despite being CAT III 600V rated is concerning. The CAT rating should ensure safety when measuring higher voltages in specific environments, but the poor accuracy and functionality negate much of the value of that safety rating.

Why This Matters (in detail)



Inaccurate Readings

The low input impedance and the AC mode issue make the readings highly suspect. You can't trust the voltage measurements, especially in sensitive circuits or when troubleshooting.

Difficulty Troubleshooting

The slow refresh rate combined with the inaccurate readings makes it much harder to diagnose problems in electronic circuits.

Safety Concerns

While it's CAT III 600V rated, the erratic behavior makes it harder to trust the meter's readings. Erroneous readings could mislead you into thinking a circuit is safe when it's not, or vice-versa.

Poor Value

If the performance is on par with a $6 multimeter, the extra cost for the CAT III rating isn't justified if the meter's fundamental function (accurate measurement) is compromised.

Potentially Damaging to Circuits

If you rely on a voltmeter with faulty measurement of voltage, you could potentially cause damage to circuits by trying to measure the voltage on them.

In Summary

You've identified some very serious problems with this multimeter. The low input impedance, slow refresh rate, and the DC voltage issue in AC mode make it practically useless for any serious troubleshooting or accurate measurement. The CAT III rating offers some safety benefit, but the unreliable readings diminish its overall value and trustworthiness. You'd be better off with a more accurate and reliable multimeter, even if it had a slightly lower CAT rating (depending on your specific use case).

Recommendations (depending on your situation)



Stop Using It

If you're relying on this multimeter for important work, it's best to stop using it immediately. The inaccurate readings could lead to incorrect conclusions and potentially unsafe situations.

Return/Exchange

If possible, return the multimeter to the vendor. Explain the issues you've encountered and request a refund or exchange for a more reliable model.

Consider Reputable Brands

When choosing a replacement multimeter, consider reputable brands known for accuracy, reliability, and quality construction (e.g., Fluke, Agilent/Keysight, Tektronix, Klein, etc.).

Review Specifications

Carefully review the specifications of any multimeter you're considering, paying close attention to:

Input Impedance

Look for 10 MΩ or higher.

Accuracy

Check the accuracy specification for each voltage and current range.

Refresh Rate

A faster refresh rate is generally better.

CAT Rating

Choose a CAT rating appropriate for your intended use.

Read Reviews

Check online reviews from other users to get an idea of the multimeter's real-world performance and reliability.*

Calibrate Your Meter: You may consider having a professional calibration lab calibrate your voltmeter. While expensive, it may save a lot of headaches in the long run. Flag for review