Your costs should be about the same, because you should be dividing your position amount by the two different trades. The statements about your costs being doubled, should be considered wrong unless you want to increase your leverage.
Except for the fact that you're paying trading fees (2x) for basically a zero position. It's basically just a breakout strategy... but instead of trading the breakout, he will be stopping out one side of his "trade". Doing the breakout strategy like everyone else would do it, entering long when up/short when down, would be less costly.
Buying and Selling the same pair, at the exact same time will always = Zero profits. But at least you wont lost anything, right? Well Well - Yes you will be out of pocket because you will need to pay the daily Libra on the Sell side of the position anyway - Maybe this guy should just try out some trades as of an example or experiencing the situation him self than as of reward - Why clarify the same point when he obviously is not listening. ?
I think in certain market conditions having both long and short with different lots size can work, and have to change the positions dynamically..