Look at the gap between repeat orders in your own data before designing anything. If a meaningful share of customers buys the same item again within a consistent window, that item is a candidate. If repeat purchases are scattered across months or land on different products each time, a standing order is solving a problem the customer does not have.
The qualifying conditions are usually the same: the product is consumed rather than kept, running out is annoying, and there is no pleasure in reselecting it. Coffee, cleaning refills, pet food, supplements and personal care fit that description. Apparel, homewares, gifts and anything bought for the joy of choosing usually do not.
Start narrow. Offer the subscription on the handful of products that pass the test, at intervals drawn from real reorder gaps rather than round numbers, and leave the rest of the catalog as one-time purchases.