Anyone use TriTats numbering ?

they work great- in that you have a bold, clear, easily readable race number on you.

takes about a week of daily scrubbing to get them off.  (granted, I've never tried polish remover or brillo pads- just soap and water in the shower)

Why not just use the number stamps like they do at Kona?

As a competitor, who cares what your body marking looks like?  It's there for race officials to be able to identify you and so you can purchase pictures. 

The tats are a PIA to remove - sharpie for me, all the time.  I always body mark myself before I leave home or my hotel room.  Race number on each arm and age on my calf and my sharpie is always in my transition bag to add if they require numbers on the thighs.

X 2: especially if you are wearing or put on sunscreen of any type.  I may be the MOP goober who tries these and pre-mark myself prior to race day. I never like standing there waiting for the old lady to mark me up and down.

Because I am a tremendous dork, I use them and love them. I will likely never be FOP, but I do everything I can to feel like a racer. Having slightly more "official-looking" numbers gives me a bit of a psychological boost, so I do it when I can. Because I am a tremendous dork.

To answer your question about which to go with, I suppose it depends to a certain extent on your size. My arms would just about fit inside a large Slurpee straw, so I go with the smaller numbers. $.02 from the cheap seats.

One of the races I do used them this year, and I thought they were great.  Volunteers got them on easy peasy, I got them off no sweat with the baby oil that was recommended on the tattoo sheet.  Definitely gave a more professional feel to the event.

I don't think I see myself purchasing them for self-use, however.  Just not my style I guess.

So did the sunscreen that I used for my race last year.

I may join you as a fellow dork.

How much do one of those stamps cost? 

I could not find something like that online- or what to call it. If you search big number stamps, you get kid stamps. I'm sure an office supply store? If anyone knows what these are, post a link or say where to get them.

I googled "ruber ink single number stamp" and got results for custom stamps.  Something 3x1 inch would cost around $12.  But I'm not sure if you could get something cheaper because the design you are looking for is just a simple number.  I'm sure the price is assuming you will have a custom design more like art work.