Margins are a hotly debated topic. Some traders argue that too much margin is very dangerous, however it all depends on trading style and the amount of trading experience one has. If you are going to trade on a margin account, it is important that you know what your broker's policies are on margin accounts, and that you fully understand and are comfortable with the risks involved. Be careful to avoid a Forex margin call.
Back tests – You can read my forex robot reviews to see if the forex robot has back tests which will give you a good idea how it performed historically, some forex robots even back test as for as 15+ years! Ideally, you would want back tests to have been done using real tick data and spreads, thus making the forex robot back test results as accurate as possible in the mt4 strategy tester