In addition to your accounting question, there may be legal issues to consider:
Is your customer legally obligated to pay the full amount once agreeing to purchase your goods ? If so, a single invoice ( possibly with two line items) or two simultaneous invoices are appropriate.
Can you sell the goods to someone else if the customer backs out of the deal? I see potential complications with only a 75% invoice that could in any way be interpreted as the total or final amount. This is especially worrisome if the goods are customized for the customer.
In all this, the size of the deal will matter. If writing off the 25% would be a minor problem, then perhaps you should do whatever makes the customer happy. But if you have a major investment by the time of delivery, you need more protection. You should consider why the customer wants a 75% invoice, because there is no valid accounting reason. If the customer has contracted for the goods, they will owe the money. You might well wonder whether they will have it when final payment comes due.