Just had my 1991 strat plus setup. The tech recommended changing the tremolo from floating to fixed (It has the hipshot tremsetter). Was not sure about that but I went through with it. Now there is a slight string buzz on the 1st and 2nd fret low E string.
So the question is, what are the merits to each? Is a fixed trem sort of defeating the purpose of the hipshot tremsetter? I kind of liked the floating myself.

If I understand your question , when you put tremolo from floating to fix , this lower the strings action. You have to readjust the height of your saddles and string touch frets.

Proceed to a fender complete set up

Take it back and have the tech re-adjust it for you for free. If the tech set it up properly to begin with it should not buzz at all.

Why is some tech/hack trying to force his preference onto you?

The problem is that in putting the trem plate flush to the body, he has lowered the saddles a fraction (barely perceptible). You need to raise the action on the strings that are buzzing.
A bit of a nonsense mistake for a pro to make. I wouldn't be going back to him.

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No no and no

A pro ?
It's not because someone like work, repair guitar that is a pro. Whether he working in his shop or a music store, it does not mean he is competent. We read many examples in this forum whatsoever for amps or guitars.
It this case this guy probably do not know how to do a se upt with a floating tremolo. Or zini2001 said yes to the Eric Clapton set up ?

Yes, I believe he either doesn't know how or just doesn't want to deal with the hipshot trem. But yes, the buzz should be corrected at least. I may have him fix it but take it to someone who knows how te set up the HT later.
How does the HT respond to alternate tunings? I sometimes drop it down 1/2 step.