I've had this calculator banging around inside my desk drawer for a couple of years now, and it still works just as good as it did the day I bought it. It almost looks as good too, thanks to the built-in hard plastic cover.
My decision to buy this calculator originally came about because I was looking for something a little more advanced than a "basic-math-only" type, and this one offered the functionality that I wanted at a good price.
In addition to several scientific functions, and its comfortably sized and spaced keys, the Sharp EL-520L also includes a a great dual line display that simultaneously displays all of the numbers that you've keyed in, as well as the result. This has come in extremely handy on multiple occasions when I've been adding up a large series of numbers and did not receive the expected result. Rather than clearing everything out and starting over, the dual line display allows me to review all of the numbers that I entered, examine each one for errors, and make the necessary corrections. This feature alone has saved me a great deal of time.
I've been using this calculator on a weekly basis since the time I purchased it, and it is still running on the original battery. This is, no doubt, thanks to it's dual power capabilities that allow it to run on solar energy when it is bright out, and on the battery when it is not.
Compared to using a plain, basic pocket calculator, I think the couple of extra dollars that I spent to purchase the Sharp EL-520L have been well worth it.