I haven't used whiteboard paint, but I have used chalkboard paint. One note from this experience: The texture in any previous layers of paint is very significant if you're trying to write on the wall. The texture in this case was from a standard paint roller; it was quite palpable even after the chalkboard paint was applied. You'll want to apply primer to the surface in thin layers with a sprayer if you have access to one, or sand thoroughly if your surface is already painted and not smooth.
Also, drywall and layers of paint aren't very durable for day-to-day use. My low-use chalkboard is weathering fairly well. After 8 months of writing the last time someone took the dog out, there are wear patterns where it doesn't erase or take the chalk as well as it used to, but it's not chipped or worn through anywhere. I erase the times once a week. If you intend to use this frequently, consider choosing a different product. Most real whiteboards are on hardboard or steel backing layers.
The different option I'd suggest is to use tileboard. Here's a 1/8" thick 4x8 panel from Home Depot for $13. It's prohibitively expensive to coat your walls in commercial whiteboards, which run from $150 to $300 for a 4x8 sheet, but panelboard or tileboard is cheap enough to coat the walls in. (Some would argue that IdeaPaint is also prohibitively expensive, but that could be debated). You can mount the panels with screws, but it will bubble. You should glue it to the wall or to a thicker piece of MDF or hardboard that won't bubble. You can also get plastic strips that clip across the gaps to make the joints less obnoxious. After 14 months of fairly heavy use as a daily whiteboard in my home office, I can say that I'm quite impressed with this stuff and will never pay the ridiculous sums that others charge to buy real whiteboards.