I’ve owned many Hinderers, all XM series, 3” and 3.5” XM-18’s and the big ass XM-24. I’ve loved them all but I no longer own all of them. I’ve moved some along to make way for others. The 3” models were too small for my XL hands, the wharncliff would sometimes nick my hand (meaty part under the thumb) when opening. It had to go, although in a way, I still miss that knife. Another 3”, a spanto was solid, but still clipped my hand in the same spot.
The 3.5’s were excellent although I had one in S35VN that was so thick behind the edge that it would never sharpen, although I tried desperately for a LONG time. I moved it along. Similarly, for reasons, I miss that knife.
Anyway, I still have a few Hinderer’s and I love them dearly, 3.5” and the big ass XM-24. For me, the ergonomics are amongst the best knives that I’ve ever owned, and that’s a whole bunch.
So, to answer your question, if you love the knife as I do, there is no amount that becomes too many. Hinderer knives are simply amazing.
Lastly I will say this, I own Curtiss and Koenig knives along with many more, and love those as well. But I will always have at least a few Hinderers in my collection. And for the record, I carry all of my knives. If I don’t love it, it doesn’t get carried, and it gets moved along.
TLDR: they’re amazing. No such thing as too many. Keep the ones you love, move the ones you don’t.