The concept is simple. If someone is reading an in-depth blog post of yours, chances are they’re very interested in what you have to say on the topic. The key is to then offer them something that is directly related to the topic they’re reading about. You know they’re already interested, so by offering instantaneous extra value it’s not difficult to see why people would gladly sign up.
The Screaming Frog SEO Spider Tool is a desktop app that you can install on PC, Mac or Linux, which will crawl websites and analyse them for common SEO issues, such as broken links, duplicate content and response time. The free version works for up to 500 URLs, or you can buy an annual license for £99/year, which will also unlock a set of advanced configuration options.
However, the targeting available in social media and search engine advertising can make it a great value. You can reach exactly the right people, and measure the effectiveness of your campaign with more precision than traditional advertising channels. Google Adwords and Facebook Ads are two of the biggest advertising platforms, but your organization may benefit from more specialized or smaller platforms as well.
I applaud your initiative in putting together a list like this. The research going into it had to have been gruesome. However, as you point out, it is not exhaustive. Just as an example: you missed MailChimp which is one of the most used email platforms; DrumUp which I use in addition to Hootsuite as a scheduler because of the ease of scheduling posts to a Facebook business page; Medium is an excellent blog publishing platform; and more. Not a criticism of your work, which I love because it points out options I have not yet explored. More a reminder to everyone else that no list like this is exhaustive.
The key here is to ask regularly rather than just once or twice. Most of your followers only see a fraction of your posts, and you should be getting new followers every day, so it makes sense to request subscriptions at regular intervals. If you can offer some sort of incentive or even just promise exclusive content within your emails, that helps too.