I’ve given both Smath and Maple a try, too. My experience is similar - Smath should probably not be trusted to calculations you will need to refer to years from now (the developer may move on to other things) and Maple is more of a mathematician/student’s tool than an engineering utility.
If you normally use Mathcad for simple isolated calculations, just for the sake of getting a clear answer, perhaps with units perhaps not, then you can probably transition to Maple or Mathematica rather easily.
If instead you normally write elaborate reports in Mathcad with things like formatted plots, tables, and program blocks, then you’ll have a much harder time. You won’t be able to just switch over everything you normally do into the other software without having to leave some of the functions you use behind.
There are, of course, other capabilities and workflows in these other programs that have their uses. You may be prefer one over another. In my case Maple and Mathematica don’t offer the simple clean output that looks like the algebra/calculus that I would prefer to put in a report, and insert loads of other code that isn’t relevant to the subject of the report. And in my case Smath doesn’t have the stability or product support for me to seriously rely on it for professional work with a variety of coworkers.
That said, if I had a problem that was very mathematically intricate, such as a spring-mass-damper system needing ODE’s I might prefer to start with Mathematica, given what I’ve seen in the demos and tutorials about setting up the problem. I’ve done it in Mathcad already but in comparison it seems easier to do in Mathematica.