So if you just get the smart speaker, then it will play songs "inspired" by what you asked.
i.e. you walk into the house and just say "hey google play some smooth jazz/sad music/hip hop/rap" it'll do that, no problems.
But If you say "hey google play songs by [artist]" it might instead play a curated playlist related to that artist (although it wont literally be songs by that artist) but usually I find it plays all the main songs by that artist.
If you ask it to play a specific song, it might complain and instead play a playlist related to that song (which will usually contain that song anyway).
With some preparation, you can also get it to only play specific songs for free
but I've never bothered with that.
If you want to be able to just say "hey google, play [specific song]" then you'd need some premium account.
So if you just get the smart speaker, you'll technically still be able to play the songs you want, just not as directly unless you use the method outlined in the yt video or get a subscription.
To give you an idea, I have a bluetooth speaker and I have a smart speaker. I dont use my bluetooth speaker anymore because the smart speaker is so convenient, even with just the free account. I can tell it to lower the volume a bit, or pause or skip, all with my voice. (And this is just music. Smart speakers can do so much more)
If you wanted to play yt on a bluetooth speaker you'd also have to deal with youtube ads before every song or an autoplay which is probably not any different from the curated playlist on the smart speaker.