This was a lovely laser cut kit from a local children's museum, Eureka. Made by Small Machines based in Sheffield UK for the museum they had a couple of other machines laser cut from mdf.
It wasn't too difficult for my 6 year old to assemble, it's just good to have adult supervision for neatness at least when gluing with the pva that they supply. To be honest I didn't have to use the pva on all of it, just the curved piece on top that guides the marble and keep the axel bar in place and not fall out at the end.
It's great to see the pistons move a marble uphill and kids be amazed. I thought it might do 2 at a time but it knocks the other off. I made a little mdf base for it to sit in so the younger kids, who might be a little less delicate and forgiving don't knock it over.