Because of their nature, informal arrangements don’t normally last more than 24 months. Therefore, they generally suit businesses that have short term cashflow issues, and a relatively small number of creditors.
Unlike voluntary arrangements, during an informal arrangement interest and charges are not stopped unless by agreement with individual creditors. So, for example, although HMRC might be willing to consider an informal arrangement, it will not stop applying interest to your debt, so the debt and interest will need to be repaid.