I spent 29,900 won for a SIM with 1GB of data (and 3,500 won remaining for calls/texts). I'm here for five days. An Egg at 8,000 won per day would have cost me 40,000 won, plus I would have had the hassle of keeping an extra device charged and/or running out of battery while out on the go. I saved 10,000 won and it's much more convenient. And each extra gig is 15,000 won, and it's pretty hard to burn through 500MB in a day (especially as the phone automatically connects to olleh wifi hotspots whenever possible), so even if you're a heavy data user, the SIM is probably cheaper than even the unlimited Egg.

I suppose if you're only on a weekend mileage run or something, the Egg is a better deal.

Although I will grant that the Egg supports LTE, which apparently the Evergreen SIMs, at least, do not.