I’ve never worked at one, but I interviewed at HRT. The interviewers were all quite kind, and more importantly to me, they asked difficult questions relevant to the role. Specifically, the role was for DBs, and the questions (beyond “can you do some basic coding”) were all low-level RDBMS or Linux. I hate Leetcode, doubly so when I will never, ever be using those skills on the job.

Given that those places are also doing stuff like writing their own network stack to reduce latency, I get the impression that they know their shit.