What I like: a lightning fast delivery. The device works. Whether it really is very accurate, I do not know, because I have no comparison. But when I used it in my practice in a patient with COPD, the device stated clearly that the oxygen in the blood was very borderline here. As the patient came from the pulmonary doctor, you could confirm the result. This was in itself very important. The unit responds very quickly. Delivered in a small Täschen. For the price absolutely fine.