Instead of an SASE (i.e., an envelop), is it acceptable to send an SAS-POSTCARD?
Sure. Just don't put "check this box" and offer four stupid responses like:
1. Not right for me
2. Really not right for me
3. Left me cold
4. Left me calling on Dog for an end to my suffering
I'm not a fan of the postcard cause I think they get lost more easily than letters, and there's less space to write anything if I'm so inclined (see 1-4 above).
The cost difference is fifteen cents per unit, so I'm not sure what the benefit is but I'm not going to sneer sardonically at a postcard. I save all that for "Miss Snark the Video Game".