The catch is the risk that HIVE price fluctuations means you might get more or less than $1 at the end. You get the average (median) price over the 3.5 day period which isn't necessarily the same as the price at the end when you receive the HIVE.

Also if HIVE were to drop a lot (around 50% from current levels) there is a haircut rule where you get less than $1 for the conversion. Given crypto volatility that isn't impossible in 3.5 days, but probably still reasonably unlikely.