My Take
I love Khaoot as a part of formative assessment. Students are able to put their names or initials in the program once you have given them the code to get in. You can print out the results for the students and you are able to see what the scores are from your students, once you get your results you are able to then use those results to help with your small groups the next day. IF you are looking at this from a technology stand point you can see this in the TPACK framework as technological pedagogical knowledge. I would highly recommend Kahoot to any teacher. I think you could use this really in any grade level but you would have to teach the students how to properly use it first.
How I Use It
I use Kahoot in the classroom as a part of formative assessment in small group as well as whole group. Most of the time the program runs very smoothly, but there are times (very few) that it'll freeze for a a minute or two but it comes right back.