I have the Cosina 100 f3.5, only relabeled as a Pentax FA
It works really well but makes a horrible racket when focusing.
The matched multiplier is cool, but 1:2 is good for me most of the time.
I’ve also tried the Raynox, with very good results on a 200mm lens in particular...
And I have a Takumar 50mm f4 (1:2 but very sharp) and a FA50mm f2.8 (1:1 and easier to use)
I’ve found for my sort of casual macro, I want a lens with ‘A’ contacts to enable p-ttl flash. Most extension tubes don’t do that.
If I was starting from scratch, I’d probably start with the Raynox then an A50mm macro.
-Eric