I understand there is a hydrofoil from Vienna to Budapest. Has anyone done this and can you give me details

Do a search here - it has been written about. I was considering the possibility but was talked out of it here on Fodors.

It has been described as a somewhat tedious and not all that exciting trip. Better to take the train - which we did.

Do you want to spend time on the hydrofoil or in Budapest? That is the question. I researched this in connection with my recent trip. The train was a lot cheaper and speedier so that is how we went.

I agree with the above advice.

The hydrofoil is old and slow. Scenery is not that great or worth the high cost.
Take the train - faster and much cheaper- spend your time and money in Budapest.

It's not one of the most scenic stretches of the Danube and, by the nature of a hydrofoil, all you can do is sit in a seat and peer out of a window. Along the more scenic parts of the river, there are ships with open decks and full catering so that you can have a meal or a drink whilst seeing the scenery.
Details of the hydrofoil are on
www.mahartpassnave.hu

I did get out of Vienna one afternoon to see Roman ruins at Carnatum (very interesting, by the way) and watched a hydrofoil go by from a riverside restaurant.

It just depends on how you want to spend your time. For some people, the boat journey is part of the fun.

Good scenery along the Danube outside of Vienna (much better than the stretch between Vienna and Bratsilava, by the way) can be found West of Vienna in the area known as the Wachau.