Two disposal spec sheets can look alike and still fit different sinks and suit different kitchens. Put them side by side and go down the same list for both. Write the answers in a column for each unit. A blank cell is a question to ask before anyone orders.
Feed style
Note whether the unit is continuous feed or batch feed. A continuous feed stays on while you add scraps through the opening. A batch feed starts when a stopper or cover is set in place. Each style has its own habits, and the spec sheet should say which one it is. Ask the seller to name the feed style in writing.
Motor size
Read the motor rating the sheet gives, usually in horsepower. A bigger motor is not automatically the right one. Match it to the amount of scrap your household puts through the sink and to the kind of material. Ask whether the rating is a peak figure or a continuous one, since the sheet may list only one of them.
Mount and fit
Check the mounting system against the sink flange you already have. Some units use a standard mount that fits most common sinks, and others need a specific ring or adapter. Check the height of the drain outlet on the unit against the height of the trap arm below. A mismatch means a different parts list and a different visit.
Electrical and drain
Ask whether the unit ships with a cord or needs a hardwired connection. Ask whether a switch is included or needs to be added. Ask what drain connection the unit uses, and whether a dishwasher inlet on the side will be connected. Write each answer down next to the model it describes.
The paper behind the model
Read the coverage terms for each unit. Note the term length, which parts the terms name as covered, and what conditions attach, such as keeping the unit on a particular maintenance schedule. Compare the terms line by line. If a point you relied on is not in the written terms, ask for it in writing before you buy.
Keep the stop point in mind as you compare. Some tasks at the sink are yours, and others belong to a trade. The disposal page explains where that line falls: Garbage Disposal: typical service life and when to plan.