A gold Expert Advisor is an automated trading program that runs inside MetaTrader and trades gold (XAUUSD) without manual input. It applies one fixed set of rules for entry, stop loss and exit to every trade, which is the whole point: gold moves fast enough that discretionary decisions are usually made under pressure, and rules made under pressure are the ones traders regret.
Profalgo builds four of them. All four trade XAUUSD only, all four run on MetaTrader 5, and all four are breakout systems: they wait for gold to push through a level that matters and take a position in the direction of the break, rather than fading it or averaging into it.
They exist as four separate products rather than one because they disagree with each other on purpose. Gold Reaper reads intraday structure on H1. Gold Trade Pro and Goldbot One wait for the daily bar to confirm. Gold Phantom runs across H1, H4 and Daily at once. Different timeframes mean different entry moments, which means their drawdowns rarely land in the same week.
That is the argument for running more than one, and it is also the reason the Gold Bundle exists. It is not a discount on four copies of the same idea; it is four different readings of the same instrument.