Two account features appear on broker sites aimed at small traders. One is useful for testing an EA. The other is a reason to look elsewhere.
Cent accounts
A cent account is denominated in cents rather than dollars, so a deposit of $100 shows as 10,000 cents and one lot is a hundredth of a standard lot. Trades are placed on real prices with real fills, and the money at risk is tiny. For an EA owner it offers something a demo cannot: live execution, real spreads, real slippage and real swap, at a cost small enough to be an experiment. The limits are that not every broker offers them, the instrument list is often shorter, spreads can be wider than on standard accounts, and the tiny sizes may not reflect fills at normal size on thin instruments.
Deposit bonuses
A deposit bonus adds credit to an account, typically a percentage of the deposit, subject to conditions. The credit cannot be withdrawn, it can be removed if a withdrawal is made, and it usually requires a large volume of trading before any related profit is released. In the meantime the bonus counts as margin, which encourages larger positions than the real balance supports, and its removal at a stop out can turn a survivable loss into a total one.
The FCA and ESMA prohibit brokers from offering bonuses and similar incentives to retail CFD clients. A broker offering one to a UK resident is not an FCA entity, and the bonus is the least of the concerns.
A trader wants to confirm an EA's live behaviour before committing £5,000. They open a cent account at a broker that offers the EA's markets, deposit £50, and run the EA for two months at its normal settings. The trade history shows real slippage averaging 0.3 pips and swap on the multi-day holds as the specification promised. Every trade carried a stop. The £5,000 account is then opened with more confidence than any demo could have given.
A cent account is the cheapest live test of an EA that exists, and worth using where a broker offers one with the right instruments. A deposit bonus is a signal that the account is outside UK protection and that the broker's model depends on clients over-trading, and neither is a place to run an EA.