The 12C calculator itself might not have Solvers... but the OmniGo does.
There are, in effect, three calculators in the OmniGo: the 12C is one, there is also a more standard calculator, and there's also a collection of Solver worksheets for financial operations and conversions.
I'm sorry I can't give you a detailed comparison between the OmniGo and the 19B or the Solvers on the 200LX, since I'm not familiar with either of those other devices.
Steve