What would be the main differences between iSpionage and Ahrefs/MajesticSEO/Moz?

Ahrefs/MajesticSEO/Moz are focused on competitive SEO and backlink analysis.

iSpionage is focused more on the competitor Adwords and landing page analytic.

Being able to see competitors' landing pages reveal much more info about your competitor strategy. You can see learn:

1. What their offer is.
2. How they position themselves.
3. What kind design theme that they use to convey the message.

So even non-search engine marketers can benefit from iSpionage intelligence.
In this internet age, you need to stand out of the crowd.

BTW, iSpionage also has some SEO data:
You can see what keywords bring organic traffic to your competitors' site.
This will help you with your content strategy.