The customer support at signkeys was very good when I had issues with our integration to their system! Great team behind it as well!! Nothing really for me dislike about them but more so because i have not yet used all features they offer within my account thus far (which can be expected from any new software).
If you're looking into signing keys - check out other options first just incase there are better integrations available elsewhere or if pricing could work differently due too services already offered outside another product? Integration between different types of data sources such as Salesforce & Xero has been seamless since usingSign Keys.