Yes, I just did it over Christmas just gone - with the New Year add-on to Cambodia which I see they are offering again for this year.
I'd recommend it. Hot British summer-like temperatures to start in Hanoi, but then getting very hot and very humid as the tour moves south to Ho Chi Minh City (and onwards into Cambodia if you do the add-on).
No need to take any cash of any type with you. There are ATMs absolutely everywhere to pull out Dongs and Riels - or US Dollars if you'd prefer. As with most countries in the area, US Dollars have to be in mint condition to be accepted, so if you do get some before you go, make sure they are brand new notes with no tears, marks, writing, wear or folds in them.
