I am not a fan of martingale system of gambling I had tried it once and ended up with a streak of losses, I am inclined to soccer betting thus I analyzed matches place an accumulated bet usually with small odd to minimize my risk, I had never seen a confirmed gambling strategy that work perfectly, it's up to every individual gamblers to use their own initiative and adopt a strict money management to have an edge over the bookies, gambling is like a fun to me because of the passion I have in soccer bettings which enable me to predict matches aside that type of betting I don't involve or participate any other form of gambling.
I tend to bet on football betting, but I don't rule out the possibility that I play on luck-based types of bets. this depends on the situation, and my mood when I want to bet. not all of them only bet on this type of football bet, it's not uncommon for me to play other games. slots, roulette, blackjack or baccarat. depending on my mood at the time, or while waiting for the football match to start.
talking about the martingale technique, or whatever type of technique and strategy it is, it is basically legal to use this technique. but in my opinion, one needs experience and not always fold the bet every round. if it is done, then, as you say. consecutive defeats would be inevitable.
so basically the martingale technique doesn't always have to be applied to every round, you can combine it in other ways.
in essence, no technique is truly effective. so the important point is, one must know when to stop and when to start again and the most decisive factor is luck.