His time with the Cubs spanned nine seasons, from 1964 - 1973. For most of that time, the entire infield was the same four guys, Santo, Kessinger, Beckert, and Banks. I think that is one of the reasons why the '69 team was so popular....most of the core guys were together for several years. The 2016 team could be the same way, with the core being young and under team control for several more seasons.
Beckert was a four-time all star and won the Gold Glove in 1968. His best season was probably 1971, when he hit .342 (which was only good enough for third in the NL). I would place him as a second level star of his era.
He wasn't a superstar, but he was pretty good. Pretty good got him in several of the other sets of the time, like Kelloggs, Dexter Press, Milton Bradley, Topps Stamps, and some of the Topps inserts. I've ended up with 36 cards of him.