The SPDR ETF rebalances monthly while the iShares ETF rebalances in May and November.
This means that a stock that grows in volatility may not get taken out of the iShares portfolio as quickly as it would the other two.
By rebalancing less often BlackRock avoids the trading costs and turnover of rebalancing more frequently, Shores said.
The iShares ETF costs 0.15 percent of assets invested annually, compared to 0.25 percent for the PowerShares ETF, and 0.12 percent for the State Street ETF.
Advisors and ETF executives tell investors to hold these ETFs as part of their core portfolios to offset risk.
BlackRock believes allocating 25 percent to 50 percent of the equity portion to a low volatility strategy is reasonable, said Sara Shores, global head of smart beta for BlackRock.
However, many investors are using these ETFs tactically.
"If you are more willing to trade in and out of the fund, you can play defensive with it during difficult times," Kalivas said.