I agree with the comments of James Smith and Ben Nathan...
I personally stay away from EA's. In the long run markets are dynamic. EA's tend to fall off over time and may cost you your account. Also, people running EA's have to compete with multi-million dollar High Frequency Trading systems operating directly from the broker network systems, which makes thousands of transactions per second... And EA running off a PC cannot compete with the speed of these systems.
As far as Demo Accounts vs. Live Accounts are concerned I wish to add my own comments as follows:
a) A Demo Account does not invoke the human emotional responses a Live Account does. This is the reason an estimated 90% of all new traders will blow up their accounts. Learning to cope with these emotions is the biggest challenge any new trader faces. In my opinion the best way to use a demo account is to formulate your own trading plan, which should include a well designed trading strategy, strict set of personal trading rules (aimed at controlling your emotions) and a solid risk/reward profile which should be developed to minimize risk (losses) and maximize profits. Once you have all of these figured out you should practise your trading discipline with a demo account and improve/adjust your trading strategy until you feel comfortable with it.... this may take some time, but treat your demo account as if it is a live account.
b) A Demo Account does not have the transaction delay's or 're-quotes' usually associated with live accounts. In some cases this may result in failed opening or closing of positions during periods of high volatility and volume. This is why it is important to have a good risk/reward profile with strict rules that you must adhere to.
These, in my opinion, are the only real differences between the two worth noting.
Hope this helps.
Keep it simple, be disciplined, get rich slowly and above all protect your equity!