I cant comment about the iwatch as i have a samsung Galaxy s4 phone and use The samsung Gear 2 smartwatch . but about smart watches in general its just another toy/ gadget . if you can get it get it. if not you not missing much ... for me it comes in handy, often i will get texts about last minute dj gigs and have to respond quickly or it will go to someone else , i can't have my phone out at work... but can send a quick pre made template text etc.... as it pertains to Riding it has a exercise app that has cycling and also a bare bones bike computer app that mimics the basic $50 bike computers/ speedometers

i also use it in conjunction with a bluetooth Headset when im riding. i get a call i can quickly look at my wrist and see who it is , then answer via the watch or bluetooth headset . im assuming the i watch will have the same functions .... it has navigation apps too, but the work from the phone and transmits the turn by turn directions to the watch ... its more useful for walking somewhere tho when you are lost and dont want to look like you arestaring at your phone looking around

Dont get a iwatch specifically for cycling, but if you need a watch in general like i did why not get a smart watch... a good regular watch will cost you a couple hundred in the least anyway