I like that it's very easy for me as an admin user, no matter how many users are in my organization or not - all of them can use this tool without any problems! The price is great too (for such quality).
There isn't anything bad about System Hub so far :) It works perfectly with our CRM solution Salesforce which we integrate into every sales process within our business unit. We have been able solve some issues regarding data transfer between different systems by using their API integration feature called "API Connect".