Back when I was leaving school and looking for a job, I came across Epic and MUMPS.
From what I read, MUMPS is actually very performant. Although other companies use it, Epic is the giant. Epic was considered a decent company to work at - good reviews, good work/life balance. The downside is mastering technologies that no one else would value. Or so everyone thought. The reality was that if you become well versed in MUMPS and the Epic stack, a lot of hospitals would pay good amounts of money to you - a lot more than what Epic paid.[1] The only catch was that Epic had a 1 year non-compete clause.
At the time I considered them, they were starting to develop stuff with Visual C++ and .NET, so there was a chance you'd learn more transferable skills.
Fun story: The first time I encountered them at a career fair, I knew nothing about them. I was a grad student. At the booth, they asked me my SAT and GRE scores and were crazy impressed, and immediately booked me for their "entrance exam". At the time (perhaps even now), all candidates had to do a written exam - they'd arrange for the university to conduct it. The exam was mostly assessing logical skills, etc. No advanced material.
I didn't know anything about Epic at the time, and was extremely turned off by anyone being so easily impressed by things like SAT scores. I didn't bother to go through with it. I was studying an advanced degree, and wanted to work for a place that was not so superficial.
Fast forward a semester later when I really needed a job. I researched Epic and it actually didn't feel so bad. I felt I would easily ace their logic exam. So I applied to them. This time, though, they made me do an online behavioral screen first. The type where they ask questions like "Are you more of a X or Y?" where you feel you're neither X nor Y. Apparently I flunked that test and they didn't invite me to take the logic test. Bummer.
[1] Not FAANG level money, but still a lot more than industry average, and a relatively cushy job with you being treated as "the expert".