AdWords Express is a simplified version of AdWords. Google introduced it because they worried small business owners may have felt Adwords was too complex and time consuming. AdWords Express was then designed specifically for small, local businesses to help them create ads that could target potential customers in a quick turnaround.
AdWords Express only works for businesses who have a Google My Business page. Ads are created and results are displayed on the GMB dashboard. The ads look the same as a normal AdWords ad and appear in the same placed.
However, while Google simplified the process in hopes that it would seem less daunting to small business owners, they may have actually stripped it of its power. By simplifying, it also took away all of the things that allow for optimized ads that will deliver conversions. AdWords Express doesn’t allow you to bid on specific keywords, but rather on categories and you cannot use negative keywords. This can mean your ad may appear in keyword searches that aren’t relevant to you. It also limits your control over where your ads may appear and doesn’t allow for location based keyword options. Because it is intended for smaller, local business, there is a maximum 40 mile radius for targeting customers.
In short, AdWords Express allows for easier set-up, but the full AdWords experience will offer better targeting, more reporting, more tools, and more control.