Does teeth whitening really make them whiter? How long does the effect last?

I feel like my teeth are getting yellower, probably because I drink coffee often, so I'm considering teeth whitening.

I'm curious if there is a big difference between DIY whitening and dental whitening, and I want to know how white my teeth actually get.

I am also curious about how long the effect lasts after a single application and how quickly the color reappears.

I'm also worried about whether there will be severe numbness or pain during the procedure.

I'm worried that I might just waste money and not see good results. If anyone has tried it, please honestly let me know your satisfaction level or any recommendations.