At .25 BTC it's not a big deal, but as the sums go up the risk increases substantially.
Huh? That's backwards, transaction fees are smaller (as a percentage) if you're sending more BTC. Number of bitcoins being sent doesn't matter, number of inputs and outputs to the transaction matters.RE: estimating fees beforehand: what is the use case where that is actually useful? What do you want the user experience to be?
And what happens if the estimate turns out to be wrong?