I found in general Big Sur takes more screen real estate to show the same information, making the display effectively smaller. Having seen no advantage over Catalina in anything I tried (which I need for my newest Macs) I probably will never upgrade and will only use Big Sur or later on any Apple Silicon Macs I might buy years in the future.
I’ve had issues with Spotlight not working at all several times on my MacBook Pro with Big Sur. I finally did a complete re-indexing of Spotlight. It seems to work fine now. That said, I find Alfred to be more accurate, more robust, and faster than Spotlight. Go figure.
Yes, it works once installed with only minor tweaking in settings. The Power Pack adds a lot of incredible features. I recommend you check their website for details.
Importantly, Power Pack gets you workflows. Alfred does some cool stuff for free, but I would argue that Power Users want the Power Pack. Alfred and Keyboard Maestro are Step Zero for me on any Mac.
I’ve been frustrated with Spotlight no longer showing the location path until I came across this article that charts all the changes in Spotlight with Big Sur. To see location path press Command and to take you to the enclosing folder Command + Return. Not at all obvious. Very nice article.
Incidentally, I’m pretty sure some other tools use the Spotlight index - so if the index is bad, that may or may not affect your other software. Worth considering.