Inserts are hoods without nice looking exteriors. As such they may be available with or without internal blowers, with mesh or baffle filters, large enough for good capture or not, etc. Reading from the mass of hood threads here should provide insight into what a hood's functions are, and what parameters are needed to assure capture and containment of cooking plumes.

Heavy cooking with hot oil or grease on induction will have only slightly less plume velocity than on gas, so the hood designed for this case will not have a lot less performance than one specified for operation over gas. Induction will allow no-odor/no-grease cooking to be performed with the hood off, e.g., boiling eggs, while gas combustion should always be vented.

To get an idea of sizes available, you may wish to tour AJ Madison's site, or download the Wolf Design Guide: https://www.subzero-wolf.com/-/media/files/united-states/product-downloads/sub-zero-wolf/design-guides/wolf-design-guide.pdf and look at inserts near the back.

Another reference by a contributor here may be found at: https://bamasotan.us/range-exhaust-hood-faq/