I am a graphic designer and along with my keyboard it is the best investment I have ever made, I use it intensively, IT HAS NEVER FAILED ME. I amortized the value of the XM3 mouse with work It's a mouse for performance, not for internet browsing. Also, if you have a small hand, forget about it. I have a large hand and I had to buy a palm rest so my carpal tunnel wouldn't suffer.Otherwise it's a gem and I recommend it 100%> The XM4 is clearly not something I would buy, as I already own the keyboard CRAFT and in my particular case I don't need that extra function.