I am worried about the odor coming up through the ventilation holes.

The structure is designed to prevent smell from ascending, and it rarely comes up.
If you are still concerned about the smell, please dispose of urine as soon as possible after urination and wash it with water each time.

■Product details
Men’s wearable urine collector AS-URI S/M/L size
https://asahi-packaging.com/products/mr-urinar/