I use a full lineup of Rotalux boxes on Elinchrom strobes, but they work just as well on Profoto with the adapter. The 69" is a great modifier. The Rotalux speedring is very fast and easy to set up, the softboxes are lightweight and portable, and the quality of light is excellent. The 69" softbox is a really nice large size, comes very close to the 74" EL Octa indirect for a lot less money.
I'd wholeheartedly recommend it. It's big though, so you'll need a good stand and sandbags or an assistant if there's any hint of wind.