I'm hoping this is an ok place to ask a question like this.
I recently had to get a new mouse because my old one broke. I couldn't get exactly what I had before but I got something fairly similar. However, I've been struggling to tune it to feel good to use. It's actually been putting a lot of strain on my arm even after short play sessions.
Does anyone know what might be causing this and how to fix it? What kind of things should I do to find the appropriate sensitivity/settings or maybe I'm holding my arm differently for some reason or maybe I need a different kind of mouse?
Whether a mouse is comfortable is quite an individual thing and depends for example on what kind of grip you use. I use claw grip and a major factor for me is weight, the lighter the better, as I lift it a lot. I had a glance at those two mice and one thing I noticed is that the new one has quite a bit larger dimensions, so that might be a factor.
Don't ignore things like chair and desk height. Using the mouse your arm and shoulder wants to be relaxed. Not having to be supported by your muscles because you're lifting your arm.
I use a vertical mouse, the wired version of this one. It helps a lot. I also have an ergonomic keyboard. The more natural positioning of my wrists really helps with the pain.
You might consider using a pinch mouse, held much like a pencil it uses completely different muscles for the movement, the muscle movement doesn't go up your arm like other types of mice. I found it quite comfortable
I had the same problem, and I really only fixed it by getting a different mouse. You can look up different mouse reviews, the only mouse reviewer I knew was RocketJumpNinja, but there are probably others these days. He had lots of comparison videos which were helpful in determining which would work best for me and my large hands. (I ended up with the Corsair Ironclaw wired. Not the best mouse shape, but it works well enough).
are those not identical? regardless, i'd recommend checking out a vertical mouse. my partner works with a mouse a ton as a 3d artist, and swears by them.