Gallardo has spent his entire professional career with the Brewers and has a career 3.69 ERA and 3.71 FIP in 214 appearances. By park- and league-adjusted metrics, Gallardo has been a bit better than the average major league starting pitcher in every year of his career aside from 2013, the year he had a 4.18 ERA. He will soon turn 29 and can become a free agent after the season.
As for the Brewers' return, Sardinas is a glove-first shortstop who hit just .261/.303/.313 in 125 plate appearances last year and is set to turn 22 in May. Knebel is a hard-throwing 23-year-old and made eight appearances out of the Detroit Tigers' bullpen last year before he was dealt to Texas. He has a minor league track record of striking out a bunch of opposing hitters as a relief pitcher but has struggled with walks and dealt with an elbow injury last year. Diplan is an 18-year-old who had a 1.54 ERA in the Dominican Summer League last year.
While Gallardo has been a better pitcher than Dillon Gee, who the Mets are said to want to trade before the season begins, the deal helps clarify Gee's market a bit more. Even though he is under team control for two years, Gee would probably not net a return like Gallardo did. And the Rangers, who were linked to Gee in trade rumors around the time of the Winter Meetings, would presumably be out on him now.