I don't know why I didn't get one of these sooner for tri events.  Not much to say except that it is easy to use and good price.

Used for a triathlon; very comfortable but the clamps are too far apart: it ripped one corner of my number right off and i had to wear the number diagonally

I wore this for my first mini-triathlon, for the bike and run portion. It was comfortable enough that I didn't notice I had it on, even after the race was done.
The little plastic things come off and you pull the string thru the race number and then put the plastic things back on. I thought it worked great for the first time and plan on using it again.
I thought it much better than having to pin my number on my clothing, because it started off cold then I removed my jacket and would have had to stop and repin  the race number.

I haven't used this belt in a race yet, but just from testing it out, it proves to be efficient and fast.  A great buy for any triathlete.