To speed up the delivery time, many companies use customization approach (In SAP terminology it is called Variant configuration) where in, the most part of the BOM components and routing operation elements could be created automatically based on the design inputs received during quote/sales order stage.
[2] ETO is a technique that is leveraged to boost sales and improve margins for those companies with customers needing solutions that are tailored to fit their own unique environment.
Testing and trial periods may also be limited by the nature of the product, the manufacturing required, and the metrics established for quality controls.
As each product is essentially a one of a kind prototype, smaller companies on either the manufacturer or client side may not have the expertise or resources to implement use-cases, user testing, or future quality guidelines.
Where possible, prior similar products may provide some guidelines as to testing and precision, but the idea of re-designing or modifying an existing design is necessarily a core requirement of the engineer to order concept.