Chengdu Panda Base: book the ticket, not the mythology
The official ticket is the constraint. Adult entry is 55 RMB, sold by real-name online reservation, released 14 days ahead, with a daily cap of 85,000. The official ticket page names the WeChat mini-program and authorised platforms including Meituan, Ctrip, Douyin, Tongcheng, Chengdu Scenic Area Shuttle and Chengdu Sightseeing Bus.
A tour can still be worth it if it solves transport or guiding. What it cannot do is guarantee Hua Hua. The panda is not a scheduled performer, and the afternoon window is a visitor observation, not an official timetable.
Klook is not a named official ticket channel; check that any tour includes entry.