Flats have two personalities, clanky when installed and warm and tight when broken in. Different strings settle in differently (obviously).
It's all personal and what we expect to hear dictates or opinion. An issue I've noticed with many players are when they initially install flat wounds. Most flat wounds need a period of break in before they settle into their (basically) forever tone. Chromes, as example, are known for their initial clanky tone (some like, others... not so much) but eventually (months) settle in quite nicely (bottom tightens and high sweeten). That experience was similar to the Fender 9050Ls that I use on my Jazzes (one of my Ps has very old Chromes).
Not all flats have the same break in period.
Some people like the clank, I do not but was patient enough to work through and now they're exactly what "I" want.
So, if you just try 'em and rip 'em off cause you can't stand the clank, you might be giving your self a great disservice. Be patient, I say (easier said than done LOL)