I've never felt the need for my own chip. The big advantage to your own chip is that you can keep it on your shoe indefinitely and don't need to remove it after the race. You could also get an ankle strap style one so you didn't have to wear it on your shoe (or vice versa.) Technically, I have my own chip now because the Marine Corps Marathon used 1-time-use chips so I could probably just count that as my own. Since I have no trouble remembering to take the chip off and turn it in at the end of the race (avoiding the $30 charge for forgetting) I don't see it as a big deal. You don't have to worry about somebody losing your chip after you remove it if you have your own, but I've never had any trouble that way.

At the ING once you crossed the finish line and worked your way towards more water, food and cokes, you had to go past a line of people sitting on stools who cut your timing chip off for you. This was nice for me, since this was my first marathon and I did not particularly feel like bending over to do it myself. i would not buy one, just use the ones they lend you.

Use the race chip. Trust me-they won't let you past the finish area without removing your chip. People on stools, like Mike said. It's no hassle at all. The chip will be in your packet. Usually there's a scanner at packet pickup so you can check that it's registered to you.

Hmm. 28 euros, that's about $41 USD, ouch. I dont recall the ING race charging me a separate fee although I'm sure it's built in to the overall cost.

Overhere you always get to choose whether to rent the chip which ads to the cost, or bring your own in which case you just give them the number. I have stickers that go with the chip to send to the race organisation so there's no mistake with the number (there's the number and a barcode on it). I've scanned it and can copy paste it into online registration forms.