Converted my 1992 Rockhopper Comp and stumbled on a magic gear. No problems yet. Great way to try it out for cheap. Some of the conversion kits come with a few different rear cogs and one worked for me.
The drop outs allow a tiny bit of play that can keep the tension. Since it's a freewheel I'm not super concerned with perfect tension, if it were fixed, I'd get an Eno which I might do anyway since I know I like it.