A martingale expert advisor is based on the martingale type strategy that came to forex from the world of gambling. Its origins are in France where it was very popular in the 18th century. The basic idea is that a gambler is doubling the bet after every loss, so the win would recover all his previous losses. It can be applied in coin flipping, roulette, etc.
For example, when you flip the coin you have two possible outcomes heads and tails and each of them has a hitting probability of 50%. According to the martingale system when you lose the bet you double your stake, so the first win would recover all your previous losses and win the profit that equals the initial stake. On the contrary, after the win, you return to the initial stake. So, the system is yielding you sure profits if you have unlimited resources (if you can double your stake until the win arrives). If this is not the case the system would generate you either the profits or you will lose all your money. Well, the more resources you have the higher probability is the system would work for you.
So, how can it be applied to forex? Well, the idea is the same if the trade goes your way you are keeping the risk at the same level for the next trade. On the other hand, after a losing trade, you are doubling the risk. Thus, the system would either generate your profits or it would blow your account. Unlike in flipping the coin game, in forex, you have the advantage to influence the winning rate and the risk-reward ratio. These two parameters can significantly improve the performance of your martingale type strategy. The risk-reward ratio has to be 1:1 or higher. A higher the parameter is fewer resources you will have to add to the trade that is following the losing trade. The winning rate should be at least 50% (like in coin flipping) but much better is if it has a higher value because it would reduce your risk doubling occurrences. Well, every risk doubling is increasing the chance of blowing the account.
However, not all forex robots that use the system will blow your account. If the trading strategy is having a higher win percentage (more than 70%) martingale system can help you to recover the losses more quickly. Some will allow you to control the risk doubling level. If this is the case I would advise you not to double it more than twice. So, after three consecutive losses accept it and go back to your initial risk. When the win percentage is high three losses in a row are a rare occurrence and it is something that you can cope with and you will not risk blowing your account.
Martingale system EA is easy to recognize, its equity chart is a constantly almost straight growing line (or almost straight growing line with large dips). It has large drawdowns. The number of the trades is usually high and the lot size amount is doubling when the previously opened position is not closed or it resulted in the loss. Alternatively, you may ask the expert producer if he is using the system or you can read it in reviews.
Due to its nature to demand high (infinite) account amount resources Martingale robots are suitable for you if you have such an account. It should be $100k or more. If you cannot afford such a large trading account avoid using the martingale system in your trading because the probability of losing all your money is too high. Speaking in other words, this system is designed for accounts with larger resources. Institutional players (banks) are commonly using martingale systems in their trading.
Therefore, Martingale EA is the system that came to forex from the gambling world. The idea is to double the risk after every losing trade. It is characterized by high trade volume, equity chart is constantly growing straight line and has high drawdowns. Very often it can blow your account. They are not recommended for accounts with smaller resources. To use it your trading account should be at least 100k. It is used by banks.