You should realize that PenFed does not own the Coverdell ESA. Just like the 529, it is a government-approved vehicle for saving for education that has tax benefits. You can invest in various accounts under the ESA umbrella or the 529 umbrella. There are differences.
ESA - you can only invest $2K per year per child. You can use that for private school in addition to college/trade school. You can put that money at almost any bank or mutual fund company. You can buy CDs, mutual funds, etc. You just need to invest it with an ESA designation. All banks and mutual fund firms will know how to do it. This is a good option because you have virtually thousands of choices for investing your money and you manage it yourself. Its cons are that the maximum amount you can invest is quite small. All earnings are tax free as long as you use it for the specified reasons.
529 Plans are mostly offered by the states. And you can invest in any state's plan even if you don't live there. Each state has limited options on what you can invest in - usually some age-based plans that get more conservative as you get older, some stable plans, and some mutual fund plans with different riskiness levels. The advantage of 529 plans are that you can invest virutally any amount in it up to the cost of college. Also, if you invest in your own state's plan, you can usually deduct a certain amount of the contributions from your state income taxes. The disadvantage is that you have less control over the investments; that is there are fewer options. Also, if your state's plan is not good, and you invest in another state's plan then you won't get any extra state tax deduction.
Hope that helps.