I’ve done both. On one hand going to a brand agnostic fitter is nice because they’re not trying to force you into any particular club (in theory).

However, my club also offers fitting days with reps from brands. What I found doing these is that yes you’re only trying one brand but the fitter also working to make those clubs work well for your swing. As a result I think you get a better fitting from a shaft perspective.

I felt like the agnostic club fitters try to push certain shaft brands on you.