Tantalum-manganese dioxide capacitors ("ordinary tantalums") still have the highest CV product (capacitance per unit volume) of the common types, making them ex

Tantalum-manganese dioxide capacitors ("ordinary tantalums") still have the highest CV product (capacitance per unit volume) of the common types, making them extremely useful. Their ESR characteristics (not just summarized, but over frequency and over temperature) are also very nice. Yes, you can get the same ESR characteristics in other ways, but they're still nice parts to use. (Aside: their ESR is higher than ceramics, and this is a good thing. Many EEs think ESR is automatically a bad thing. Do not trust anything those people say about capacitors!) Ta-MnO₂ capacitors do have that one, minor, tiny, insignificant problem of starting on fire sometimes. This is not actually much of a problem anymore because people have learned how to build these things well (they're 100% screened at manufacturing), specify them (derate to 50-75% of nameplate voltage, modified by max temp), and protect them (surge/inrush current is mostly what actually ignites them, so let's not do that if we want them to live). The easiest way to use them well is to keep them inside designs (i.e., on internal signals and rails, don't let things off the board dump current through one) and they'll be fine. They're great, and every designer should use them when appropriate!