Has anyone heard of this, and if so, how hard is it?

Easy to make, goes on smoothly, smooths like satin. Takes less sweet and much better than powdered sugar/Crisco based buttercream. Here is the recipe I use.
http://forum.cakecentral.com/cake_recipe-2426-Italian-Meringue-Buttercream--Shirleys-Method.html

Does it crust at all? Can you use the hot spatula method on it to smooth out?

You may want to try Swiss Meringue Butter Cream (SMBC) as well â easier to make in my opinion than IMBC, and the egg whites are for sure pasteurized. Taste-wise, I canât tell a difference once on the cake. This is the recipe I like the best, it's very easy:

Neither of them crusts, but it does get reasonably smooth. Yes, you can use a hot spatula, but it slightly discolors the butter, it ends up with a touch of yellow tint from the hot spatula.

Edited to add: Cake covered in Meringue Butter Cream must be refrigerated, but it tastes best after itâs had a chance to adjust to room temperature, depending on the your weather, half hour to an hour should be fine.