Yes, its true, bare attention to the defilements such as — When a lustful mind is present he knows, "There is a lustful mind" (sarāgaṃ vā cittaṃ ‘Sarāgaṃ citta’nti pajānāti)
or when an angry mind is present he knows, "There is an angry mind" (sadosaṃ vā cittaṃ ‘Sadosaṃ citta’nti pajānāti)
— is not enough to remove the defilements completely. It will be enough to expel lustful or angry thoughts as long as one is maintaining mindfulness only.
Still, one should do it whenever, and wherever one can to avoid accumulating unwholesome kamma (lustful and angry thoughts on the mental level that do not lead to speech or actions, are the unwholesome mental kammas of covetousness and ill-will).
To bring about deep-rooted changes to one's mental habits is not easy. The initial stage of noting is only enough to gain Purification of Mind (citta visuddhi)
by suppressing the five hindrances. However, if we continue the process of mental noting throughout the entire day without a break, not missing anything, and if we can sustain this mindfulness over a period of days, weeks, or months, insights into the three characteristics of the mental and physical process can arise, leading to higher stages of insight such as Knowledge of Comprehension
Unless we can gain the third stage of the Noble Path (Non-returning), the root of lustful and angry thoughts is not destroyed, so they can always return whenever we are unmindful. We need to be realistic, and very patient and very determined to persist with our practice whenever a suitable opportunity arises.
If possible, try to attend at least one ten-day course every year. For lay people, it may be the most effective way to make significant progress because there are just too many forces dragging the mind down to the defiled state during everyday life. Even for a monk, living in the city, but largely isolated from society, there are occasions where mindfulness can be lost. If a lay person can achieve insight while immersed in the worldly life it is all the more praiseworthy.