not had any personal experience but i understand that the original circlip is not very good , make sure its an external circlip for a shaft. heard of people making a sprocket cover so they can keep on it.
Unless it has been meticulously looked after.......After having a nasty expererience on the outside lane of a 70mph dual carraigeway, I'd say avoid. Once wear sets in the circlip will pop off more regularly and whatever you try as a bodge, it isn't permanent. It's not worth the risk. The shaft splines also wear so even if the circlips stays on, the sprocket \ shaft splines will eventually go.
I have the earlier model with circlip sprocket, I reckon if you keep up fresh enough sprockets to prevent so much spline wear on shaft, and make sure o-ring is behind sprocket to allow presure on circlip, they should be fine. I have read elsewhere that there's a few better things with the earlier funduro, like build quality on some items. Not to mention temp gauge instead of clock, and direct mounted indicators up front.