Iridium plugs are supposed to add more power, reduce emissions, last longer, blah, blah, blah, but I have yet to hear of anyone who can supply me with any real-life data.
Some people swear by them and tell of the transformative quality of them, others are less impressed.
I fall within the second group. I've run two iridium plugs now and have noticed no difference in power, economy or the ride. I was quite careful to measure the economy and noticed on average, no difference.
Others might disagree.
However, one thing to note on a single cylinder is that the spark plug is a critical item that needs to be in tip top condition and I would much more prefer to swap the plug at every service for a brand new standard one than keep an iridium plug in place to the service change point.
Quite an opinionated point there but worthy of some thought.