Depending on how they structure the ETF, you may not have to worry about taxes until you sell it. That could be a good deal. Otherwise the turnover could be a problem in a taxable account.
However, the problem with most momentum funds (and most actively managed funds in general) is that they hold way too many stocks to ever hope to outperform. They are too diversified. There's probably less than 100 stocks for a value investor or momentum investor, that are worth holding. Yet most funds have hundreds if not thousands of stocks. Part of this is so that they can manage a lot more money. You can't jump in and out of 50 stocks when you are managing billions of dollars. So they go for 500 stocks and dilute their investors' returns.
On top of that, most funds, even if they say they are value or momentum or growth or whatever, still weight the fund according to market cap. MSCI World Momentum says they incorporate momentum into the weighting but they also use market cap. This dilutes returns over an equal weight or pure momentum weight. Market cap is the worst weighting method however most use it for liquidity reasons.
More info here:
http://www.dualmomentum.net/2014/11/individual-stock-momentum-that-dog-dont.htmlDorsey Wright has some momentum ETFs that are more concentrated (I think around 100 holdings) but they don't have a world ETF, they are split into US large, US Small, Int'l Developed and Emerging Markets.
I wouldn't worry about the strategy changing on you. I don't think they would change the look-back windows from 6/12 to 3/6 or whatever. Most of the momentum research is in the 6-12 month timeframe so I would bet they stick with that.
If they lowered the number of stocks, equal weighted it and rebalanced it monthly, I'd probably be all over it (but then I'd also want them to close the fund so the strategy continues to work well!). As it stands it's probably not a horrible implementation but for the individual investor it could be a lot better.
