Why should I Upgrade/Flash my tplink Archer A7 v5.0 to openWRT?

Hey folks,

I have had this Archer A7 for years and it works fine. I've been tinkering and changed my DNS, but read about openWRT.

I'm also building a NAS/media server. Should I leave the router as is with stock firmware or is there a performance/security benefit to switching to openWRT?

Also, if someone can point me to a guide that would be amazing.