what diffuser are you referring?
different light modifiers has it own pros and cons, depend on your usage.
different situation need different kind of light treatment, it make no sense for using omnibouce or bounce card to shoot a subject at 15ft away at a open area, (high ceiling, no ceiling or outdoor).
so you need to know how they work, and use them accordingly.
If you want a more durable DIY bounce card, just use those white PVC material. NUS SDE co-op has them in huge A1 or so sized sheets. $3.80 for one but i think can cut like dunno how many bounce cards from that man.
Anyway, having used diffusers like the Omnibounce and LSPJ II as well as DIY bounce cards I'd have to say each is good for a certain purpose. The LSPJ II is basically useless outdoors, even with the dome. Firing through the dome directly is worse than using an omnibounce.
Omnibounce is good for diffusing light at close distances (like in macro work). At longer distances, indoors, the LS is much better.
DIY bounce card is of course the cheapest and most portable. It's also the most useful outdoors IMO. Just bend the card slightly forward over ur flash head (to reduce the amount of light being sent straight up) and whack ur ISO to 800 or 1600 and you'll be surprised how far the light is thrown even outdoors in pitch dark conditions. And it still looks better than using direct flash.