I would not use anything that doesn't mix with a hardner... I am familar with what you are using... and I intend to cover this is my tutorial but I will tell you also.... Some people I have had some measure of success with some other materials... I have seen spackle, plaster, putty, glaze, paper mache... its all in what you are comfortable working with.. if you don't like the level of detail you achieve with one material, try another... but here is my rant..
Typically when you have a large area to fill. you would use Bondo Putty (kind you mix with a harnder) to fill any large low spots. You rough the bondo putty to shape with a rough grit sand paper, for the application you use with the size pieces we have, I would reccomend 80 grit. Once the Bondo Putty is roughed to shape, you would then skim the surface witha layer of Glaze to fill the voids and pin holes. The reason I used Glaze everywhere is it is what I had avaiable to me at the time, and I prefer working with it, as it produces a nicer sandable finish in my opinion... that tube of glaze/spot putty doesn't use a hardner, and can sometimes be unpredictable... Its only meant to fix small areas really, but I still never use it. You may also find reference to people mixing resin with Bondo putty, and making "mud"... this is an old timmer's body work trick to make something similar to a glaze. You can now buy ready made glaze, its a bit more expensive than putty, but I would rather have an easier time sanding my piece, than fightinging hard hard bondo putty.
I was gonna say 
