Flippity.net's random name picker is a great one as well and my blog post from August 7th about it can be found by clicking here. Flippity's also allows you to make "teams"/ groups between 2 and 12.
The Add-on is very simple to use. Directions are followed underneath of the embedded 2 minute and 2 second YouTube video.
You will need to make a copy of the template.
Select Add-ons > Group Maker > Start > Continue > Allow
Then Enter the group size in B1 > Paste roster in column A > Press the make groups button
Any questions, please let me know!