Questions about 4k players

Hello, I've been roaming this sub long enough to know apparently the only real options for a good player are Panasonic but even those have freezing issues.

Do the players read off the disc in real time or do they have onboard ram to kinda work like a short term SSD?

Are Sony players actually bad? I see that they seem divisive due to cooling issues, is this only a problem in not well vented areas or is it an unavoidable design flaw?

I currently only have a PS5, which aside from not having Dolby Vision making some movies too dark, its never had an issue. Is this because the game console is already designed to play 4k games at length so is it just built better?

Sorry, I'm looking to pick up a player and I don't want to cheap out but also 400.00$ on a player isn't what I would consider pocket change.

Is this a buy once cry once type of situation?