it's not really beta stuff though.
what they do is serve a portion of the visitors version A.
then they serve a portion of the visitors version B. then they see in which one resulted in more sales/longer engagement.
neither one is technically beta, but more like an experiment about what works to get you to do the wanted outcome.
there's plenty of tracking/logging companies providing easy facilities this and if you work in startups you'll see it pushed on your face, even if the a and b versions don't have enough difference and the sample sizes are too small to make any conclusions on. but it gives people to do something when they don't know how they should further the sales/engagement and it's on the "book" of marketing.