I consider it one of the worst purchases I have made, both in terms of functionality and the quality of the device, as well as its actual value. Specifically,
1. Functionality: it cannot replace floss or toothbrushes in any way - let alone a dentist's cleaning.
2. The quality of the device is completely cheap (made in China), consisting of components made of thin plastic that you think will break at any moment.
3. The value of the device does not correspond at all to the quality of construction (it is not worth more than 50 euros).
4. The container holds 600 grams / 21 oz of water, which empties in less than 1.5 minutes of continuous use at high intensity (10).
5. With much less money, you can buy an electric toothbrush that offers a fairly good cleaning.
Advice: it has no usefulness

Polu kalo ergaleio dunati piesi kanei tin douleia tou an eisai kai esu apo autous pou bariounte to nima to protino anepifilakta

It's worth its money.
You put it on 1, in your mouth, turn it to 10 and follow the gums. Easy.
Also, put some mouthwash in the water container for better results and occasionally pass vinegar through it to clean it from salts.

It is the best you can get (from Germany or any other country that has it at half the price) for real cleaning

Purchase from abroad good construction very good cleaning worth it but quite uncomfortable to use. In order to avoid filling the mirror and your bathroom with the water it throws, you must (according to instructions) have your lips slightly closed, resulting in not being able to see where you are cleaning except for the sensation on your gums for approximately where it is pouring water. Therefore, you cannot see where you are cleaning.

If you have space on the sink to place it and a power outlet nearby (about a meter away), it is worth buying. A little expensive for purchasing from Greece, of course.