I have a rock tumbler that I got as a present. It's neat, but this page is right - it takes
a long time, and you end up using a lot of grit as well, and it must be done in order. Oh, and did I mention that it's noisy? Definitely not a hobby for ... me.
But! One thing I have found interesting is that you can make your own "sea glass", by breaking wine or beer bottles, and tumbling the big-ish chunks. The thicker the glass, the better, of course. I'm experimenting with just using some sand as the grit material; the glass doesn't come out shiny and smooth, but it definitely wears down the sharp edges.
(And I run the tumbler thing in our detached garage.)