If you limit your trading to this period, it's a really good deal. Can't speak to the usability of their platform or the reliability in execution. During regular periods, their pricing schedule is more than my broker for some trades and less than for others.
ETF's also seem to be the new frontier for no commission trading. Schwab, Fidelity and Vanguard have a small number of them. On Friday, TD Ameritrade announced a list of 101 commission free ETF's. And no, I don't trade there
Interesting is the fact that they don't seem to limit the decent volume ETFs as they do in the some of the other "offers". My suspicions are that they offer these to drum up activity in some of these lower volume ETFs. Fidelity offers IWM and EEM (no QQQQ or SPY), but the others are pretty low activity. The TD Ameritrade list didn't even have IWM or EEM. Not sure about Schwab or Vanguard.
Being able to "trade" some ETFs for free could be helpful. The AMTD fine print reveals what a pitiful scam their deal is. Read the following: To trade commission-free ETFs, you must be enrolled in the program. Eligible ETFs purchased commission-free must be held for at least 30 days. If you sell an ETF within 30 days of being purchased commission-free, a short-term trading fee will apply.
I looked through OP's link trying to find the fine print. Nothing. It's there - probably in the appllication process. Their data and misc. fees don't look very good. Every time I look into other brokers, I find that IB is still the best for me. I have a backup broker, but I'm not satisfied in this area - still looking for a good backup.