Unless the questions are going to be really simple or all about how the president, as an individual, feels about this or that, then I think things would go much better if they gave him some time to really figure out the answers and double check facts and figures.
Otherwise it will come down to how well the president has memorized facts, policies and figures about whatever the questioner is asking, and frankly, that's not the president's job; he has a staff for keeping track of things like that. I don't want the federal executive wasting time "cramming."

Demanding that the answers be created on the spot means they're likely to be less accurate and less useful. It's likely to tell us more about how good the president is at speaking than what's actually going on. It also would almost certainly devolve into a monthly game of "gotcha" played by hostile congressmen who had time to look up obscure inconsistencies in executive policy, and that would get old really fast.

I think the idea is a good one, but that the questions should be submitted at least a month in advance. The administration shouldn't be allowed to ignore questions they don't like, but they should be allowed time to figure out what the answers are.

__________________
To educate a man in mind and not in morals is to educate a menace to society. -Theodore Roosevelt