I used to use Kahoot for teaching my college courses but switched over to Slido for ease of integration into PowerPoint. It is very effective and the students enjoy the interactivity. HOWEVER, one of advantages of Kahoot was that I could share the review quizzes with the students so they could use them as study tools.
I think Slido would benefit from more flexibility in terms of how the quizzes, surveys, etc. could be delivered (i.e. able to be left open of the course of an event vs only live).
It is frustrating that this is not an option with Slido, especially given the yearly cost.