A similar fund already trading is the PowerShares VRDO Tax-Free Weekly Portfolio (PVI), which launched in November 2007. It has $333 million in assets under management. It’s up 0.4% year-to-date.

As an investment vehicle, muni ETFs have a lot going for them. Generally, fees are about half of a municipal bond fund-0.20% to 0.40%, compared to 0.50% to 0.80%. Right now, even if it’s just half a percent you’re saving, that’s a lot of money.

Muni ETFs are also more transparent than most bond funds, which only have to report what they held last quarter. They’re slightly more liquid, too. Unlike mutual funds, which can only be sold at the net asset value of the prior day’s closing price, muni ETFs can be sold at the prevailing price any time during the day.

Read the full filing here.