"You can have the target-date fund act as your core but then put some [of your money] in mid-cap stock funds or small-cap or whatever works," said Mullins at David Mullins Wealth Management. "It can make sense … but your time horizon should be the largest factor."
One previous complaint about target-date funds—their relatively high fees—appears to be gradually disappearing.
Read MoreHow much is that mutual fund costing you?
The average target-date fund investor paid lower fees last year for the sixth year in a row, according to Morningstar. In 2014 the average expense stood at 0.78 percent, down from 0.84 percent in 2013. In 2008 that figure stood at 1.04 percent. By comparison, the average expense for all mutual funds at year-end 2014 was just above 1.2 percent, Morningstar has found.
"These funds are working despite their shortcomings," said Burkett at Palisade Investments. "If you had to pick a generic medicine off the shelf that cures most colds, you'd probably pick it," he added.
"That's kind of how target-date funds are."
—By Sarah O'Brien, special to CNBC.com