I don’t have any circuit playgrounds. What can I use or do with my high school kids for this unit?
That probably depends on what you want to do. I know that some teachers have had success using http://adafruit.makecode.com and some of their lessons, but those lessons are not integrated with the code.org curriculum. It would give them experience with a virtual playground, though.
Other teachers skip unit 6 and do the Artificial Intelligence unit (unit 7). I think either of those options could be fruitful depending on your students and what you think best for them. If you choose the Make Code option, you may want to preview several of the tutorials and select one that all the students would do and then have them pick one or more of their own to do.
Good luck!
Mike