For a relatively new company, Kartra’s interactive customer support is quite good. They have a typical ticket system in place and a growing Q & A section which they hope will cover most customer questions eventually.
Turnaround times for tickets raised is approximately 24 hours.
Fast growing companies usually struggle to keep up with support demands as staff must be trained up. It seems Kartra are handling this consequence of growth pretty well.
Given the breadth of different features, they have their staff are knowledgeable across the board.
Maybe others have had different experiences, let me know in the comments.