I have found both strategies to work. I have also found that different niches respond differently. The health niche for a specific disease my respond differently than a health niche for general nutrition. You should by all means REST TEST TEST. Never stop testing in any marketing communication.
You should focus on building your list. Do not expect sales. Although sales do happen sometimes on the first contact. There is an old saying among direct response marketers that "Money Loves Speed" When someone opt-ins to your list, get after it. Don't delay. Whether your strategy or tactic is to begin throwing offers at them or if it is to deliver value and then ask for the sale; you have to follow up FAST.
Here is a detailed tutorial about buying traffic on Udimi
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