Thanks :)
Its been brewing for a while, but didn't make sense until DEC/ECR and Neutrals arrived.
I think it'd also go some way to addressing mismatch concerns, eg, between a player who just stumbled out of silver, and another who just slipped from Diamond.
A higher ranked/better equipped player is less likely to take the offer; while the lower ranked player can choose to sacrifice potential DEC to get an advantage.

That said, a free card isn't always an advantage.

A Grumpy Dwarf as tank, for example; could be a disadvantage, even at max level.
If you take the offer and your opponent declines and fields an Exploding Dwarf (ensuring sufficient speed to go first), between Blast and Trample, you're going to lose the Grumpy Dwarf and almost definitely the next card too, in the very first move of the first round.

How do you code a bot for that? Tell it to always decline particular cards? Always accept?
Tell it to only accept that particular card when Red splinter is unavailable? Only in Reverse speed? Only in matches with Mana cap below 22?