I disagree here. The point with clay is temperature stability, for longer, slower cooking. Cast iron is better for some things...clay for others. It's not better or worse per se. Clay...braises and stews. Cast iron...sautes and stir frys.
Clay is usable on a gas stove...electric, you want a diffuser. But I use an Imusa ceramic tagine regularly. One thing you don't want, is to get it hot while empty. That's going to risk cracking it, unless you get full-on flameware...and if there is a flameware tagine still out there, it's gonna run $200 easily.