Yep - they are amazing ! They have been around for a long time - I remember going to the Model Engineer's park in Sydney when I was about 10 years old & being stunned by them. I re-visited the park with my grandchildren some 45 years later, & there they were again (but probably a lot faster) !!
Its a weird experience - when they get up to full speed, you literally can not see them - all you have is that cyclic shriek !