How so? Please enlighten me more about this possibility. It sounds interesting. I don't intend to use it. I just want to understand because there is a house edge. So if you are betting on >50 and <50 at the same time, there's no way you will lose but there's also no way you could make money. Please correct me.
If I remember correctly, the advantage is given by the martingale strategy for both outcomes simultaneously. That is, in fact, you are playing against the fact that you will encounter an abnormally large series of identical results and you will not have enough money for the next bet. That is, mathematically, this is a normal martingale, but your winnings are x2, which gives you an advantage.
However, if you want to try this strategy, check it first on simulators - I tested many different options with different parameters and I'm not sure if I remembered the profitable one.