Shark NV581 vs NV583
images from manufacturer

The only difference between Shark NV581, NV581Q, and NV583 is the accessories they come with, otherwise they are the same.

Shark Navigator Powered-Lift-Away NV581 includes a Pet Multi-Tool, Duster Crevice Tool, and Dust-Away Hard Floor Attachment with 1 Microfiber Pad.
Shark Navigator Powered Lift-Away DLX NV581Q includes a Pet Multi-Tool, Duster Crevice Tool, Dust-Away Hard Floor Attachment with 1 Microfiber Pad, and Canister Caddy.
Shark Navigator Powered Lift-Away Deluxe NV583 includes a Pet Multi-Tool, Duster Crevice Tool, Dust-Away Hard Floor Attachment with 1 Microfiber Pad, Appliance Wand, plus Pet Power Brush.

The Pet Multi Tool is a 2 in 1 cleaning tool. The hard bristle brush remove debris off surfaces, and the upholstery tool is for removing pet hair from upholstery.
The Duster Crevice Tool is also a 2 in 1 tool. You can use it as a crevice tool to clean tight areas or use it as a dusting brush.
The Dust-Away hard-floor attachment with a microfiber pad is designed for picking up and wiping away fine debris from hard floors.
The Canister Caddy allows you to transform your vacuum into a canister, so you do not have to carry the lift away pod while cleaning.
The Appliance Wand helps to clean areas under hard-to-move appliances and furniture.
The Pet Power Brush helps remove pet hair and dirt from upholstery and carpeted surfaces.