Those guys have been around for some time , they are using chemical jet technology .
They have a max burn time of about 50 seconds .
There is a chap in UK developing a ducted turbine based pack , develops about 360 bhp and burn time of 10 minutes !
Be nice to see that fly http://www.jet-pack.co.uk/content.aspx?guid=c66aca5a-b734-493f-94f0-b1188dd24ae0