Recently purchased a 2014 NX300h. After about a week I started to get a horrible mouldy smell through the vent on startup.
My experience is that aircon bombs are a complete waste of money.
I had the same problem in my Toyota Auris, I purchased the official Toyota "airco" foam 500ml cleaner. It comes with a long plastic pipe and metal nozzle with fine holes.
You can remove the glove box and access the evaporator drain in the passenger foot well (Seems identical design on my Auris, Prius and NX).
Follow the instructions on the can but basically you disconnect the rubber drain pipe, insert the nozzle right inside the evaporator and empty about half the can into the system. It fills the entire inner workings of the evaporator with expanding foam and kills all the nasty bacteria.
Fit the drain pipe immediately back and leave for an hour and the foam changes back to liquid and runs out the drain onto the ground under the car.
Satisfying job well done, no more nasty smells. I also fitted a new pollen/cabin filter to also prevent re-occurrence.