The two most popular services for those social proof widgets are Provely.io and Useproof.com.
I do have data that shows the use of those widgets tends to boost conversions.
While it is possible to use fake information with one of those apps, both do offer genuine user behavior as part of the service. The way it works is that it captures data from order forms, or lead forms, and then displays data about recent conversions.
Is it a gimmick?
Yes, I believe it is a gimmick. It is just as effective as using reviews and testimonials, it has a measurable impact on a significant percentage of users, and less of an impact on others.