For Martingale EAs, here are some personal tips to manage risk:
1) Open multiple small trading accounts to trade different pairs (Preferably cent accounts)
2) For more volatile pairs (like GBP and JPY pairs), use bigger grid size and smaller lot size
3) Withdraw your profits regularly. In other words, treat your accounts like a "dividend stocks" rather than "growth stocks". Never be greedy!
4) Diversify across cross pairs besides the major pairs (Eg AUDNZD, EURCHF etc)
And yes, it is also wise to diversify trading strategies to include non Martingale EAs too in your trading portfolio. So far for non Martingale based EAs, I like Life Changer and Market Maker.
May the pips be with you!