It was only a matter of time before ETFs, or exchange traded funds, came in life-cycle flavors. Brokerages started offering life-cycle mutual funds, or target date and target retirement, a few years ago and they’ve become very popular options for folks who want a simple investment product that does all the work for them. No asset allocation, no rebalancing, the brokerage, in its infinite wisdom, handles all that for you based on the target date of the fund you choose.
Life-Cycle ETFs differ from life-cycle mutual funds in the same way as ETFs in general differ from mutual funds. The cost trade-off is usually in the expense ratio and commission charges. With a mutual fund, you pay a higher expense ratio but have little commissions (for example at Vanguard, you can buy most Vanguard funds without paying a fee). With ETFs, you pay a commission per trade but less in expense ratios.
Otherwise, they’re pretty much the same.