Paying bloggers for direct advertisements is a bit of a grey area. It's grey because loads of brands are doing it, but it's such a difficult thing for advertising regulators to monitor.

Check out this guide so you're aware of the guidelines and risks: https://www.ftc.gov/system/files/documents/plain-language/bus41-dot-com-disclosures-information-about-online-advertising.pdf

You should also be aware of the SEO risks to your business. In short, if you get caught paying bloggers to write about your company and those articles contain links to your site, you're at risk of receiving a manual penalty from Google. See this for more: https://support.google.com/webmasters/answer/66356?hl=en

Risks aside, those tactics you noted are fine, and can work great. Depending on your product or service, You might want to consider signing up for a variety of the affiliate networks out there such as ClickBank or Affiliate Window.

Lastly, the best way to get them writing about you is to make them a part of your growth. Find relevant bloggers in your niche and recruit them as your product testers and focus group. If they feel a part of it, and your product or service genuinely enhancing their lives (or the lives of their readers), why wouldn't they write about you?