Every "interactive whiteboard" (brand and design) I've ever used sucks.
The best setup I've used so far is a standard whiteboard coupled with a projector (ideally with a second board to the side). It needs very regular cleaning to prevent a blurry display, but being able to write normally (being able to see what you're writing with zero lag) is a huge benefit.
If you really need at-board interactivity (as opposed to keyboard+mouse at the PC, or wirelessly, or casting from a tablet, or...) then Epson do a projector with an IR "pen" that works with any old whiteboard.
The best setup I've used so far is a standard whiteboard coupled with a projector (ideally with a second board to the side). It needs very regular cleaning to prevent a blurry display, but being able to write normally (being able to see what you're writing with zero lag) is a huge benefit.
If you really need at-board interactivity (as opposed to keyboard+mouse at the PC, or wirelessly, or casting from a tablet, or...) then Epson do a projector with an IR "pen" that works with any old whiteboard.