In short, the device works is very easy to use and reliable. What I like very much the clear, large and easy to read display. The case looks high quality finish (rubberized surface.) A friend of mine, the police officer, it had also compared with an official Dräger model. The measured values were almost identical. One should mention, however, the fact that for each test (similar to police checks) a new mouthpiece should be used (for reasons of hygiene, as well as for the measurement accuracy). The TM-7500 uses here the good mouthpieces with rebreathing lock!
Conclusion: The device I can recommend any of a purchase decision intends and is unsure. I would buy it again at any time.