The downside is that when you put in a limit buy the exchange puts your money into escrow until the order is cancelled or filled. Since a crash like that is unlikely to happen (first time on that exchange I believe) it just means you have money tied up when it could be put to better use
And they could reverse the trades and null them out on both sides. Just because the order gets filled doesn't means it'll complete. Until you get the asset, sell it, and get your cash out of there, you're still at risk.
