The only difference between FBS live/real MT4 and Demo would be the slippage and market liquidity.
FBS does offer same conditions in Demo accounts as live/real ones though, MT4 demo does not reflect market liquidity situation in the demo trading.
Meaning that regardless to the deep/low liquidity of the markets, all orders will be executed at the price you are looking at the moment.
No slippage in Demo
As there is no liquidity concerns in demo trading, there is no slippage at all.
Normally, if you place an order with larger lots like 20 – 50, slippage happens in most of cases as a single broker cannot secure that much liquidity.
Normal brokers have 10 – 20 lots for the tightest spread they offer.
Meaning that only 10 – 20 lots of orders at the moment from all traders around the world will be executed at the spread displayed in the platform.
Demo and Live are different
Because of the above reason, if you run the exact same EAs in demo and live accounts at the same period, there will be different profit results come out later.
So you may not want to use the demo to see your profit/loss, but it is for trying out the platform, the spread and etc.
For more information or inquiries regarding to trading conditions on FBS MT4 and MT5, please contact the customer support from the Official Website.