Back at their heyday, there were those that bought the HP 41c because it was the ultimate calculator, only to discover that the cheaper HP 15c had many more functions, and more conveniently located in the keyboard. Some things that the plain HP 41c did not have:
-extended factorial (gamma function)
The user of the hp41c could lie to himself “I can have all that if I buy the right modules”, but that would be an enormous money outlay. It must be said that the advantage module provided most of that missing functionality, but it was never as well integrated as it was on the 15c.
both competitors face to face. Forgive the picture quality!
For example, the complete 4-level complex stack in the 15c; or how well integrated were the matrix functions and the “user” mode to automatically change the pointer for matrix data entry; or the clever use of the permutations and combinations keys for matrix transformations. It really was a clever and elegant device, and still is: more than 25.000 units of the new version have been sold since September 2011.
The only two things where the hp41c always got the upper hand was in alpha capabilities and connectivity. (In fact, it can be argued that it has never been bettered in that area, the USB connection of the 50g family being a poor shadow of the many modules and printers that the HP 41c could drive).
30 years later, the HP 41c user got vindicated - finally. With the “CL” module, you have access to all the functions ever created for the HP 41c in the different modules - all at the same time.
My preferred current set-up (that is good for my work and my hobbies at the same time) is Advantage pack, Sandmath module (latest version) and HP 41Z module (the Z module has a much better complex support than the advantage pac, in my humble opinion - thanks Angel Martín!). With it, I can say I have let the HP15c behind. But it has taken ages and effort!