Check the everyday trade-offs of a storage ottoman
A storage ottoman can hold blankets, support tired feet or act as an occasional surface. Check which of those roles its construction actually supports.

Look at the lid before the fabric. A loose top lifts off completely, a hinged one needs room to swing, and a reversible tray may change how the ottoman can be used. Each arrangement creates a different daily routine. If a heavy tray of objects sits on the lid, the storage below is no longer a quick place to put away a blanket.
Measure the internal cavity rather than estimating from the outside. Upholstered walls and a thick lid can reduce the usable space considerably. Fold the items you intend to store into a stack and measure that stack. This is especially helpful for bulky throws that look compact when draped over a sofa but take up a surprising amount of room inside a box.
Decide where it will live
Mark the full footprint in front of the seat. Leave a comfortable route around it and check whether drawers or nearby cabinets can still open. If you plan to move the ottoman frequently, find its empty weight and think about the additional weight of the contents. Small feet do not guarantee that a large upholstered box will slide easily or harmlessly across your floor.
Compare its height with the sofa seat. Preferences vary, so use a sturdy existing object of similar height to understand what feels comfortable for resting your feet. Do not sit on an ottoman unless the manufacturer says it is designed for seating and provides an appropriate load limit.
Think beyond the styled tray
An upholstered top is not a level tabletop. If the ottoman will hold drinks, check whether the supplied or chosen tray sits securely and whether that use is suitable. Keep hot drinks where they cannot be easily knocked over. A small side table may still be the better place for a mug, even if the ottoman occupies the center of the room.
Read the upholstery care instructions, especially for a light color. Storage for shoes or outdoor items asks more of the lining than storage for clean blankets. For a hinged model, inspect the closing mechanism and follow its warnings; never assume a soft-looking lid cannot trap fingers.
If the main reason for buying is storage, choose access you will actually use. If the main reason is a footrest, do not sacrifice its comfortable position to fit a larger cavity. Naming the primary job makes the smaller compromises much easier to judge.