Well, first before I get into anything, I want to point out that sidequests - although time-consuming - should normally done, cause the rewards will always help you. Now anyways, the trading sequence - aside from a few annoying timed parts - is an overall very easy thing. You might run across Hyrule multiple times, but the fact that you have Epona makes it less of a bother. The reward - the Biggoron sword - is definitely one of the best weapons in the game. It does 2x the damage than the master sword and even looks cool.
Although you sacrifice using a shield, the sword is so powerful that a shield probably isn't needed. Like you said, it can't break and the fact that it's there forever is nice to know. Overall, the trading sequence was easy and the reward was well worth the 30 minutes or less you spent doing it.