I don't have the Stihl, but I do have a similar combi Ryobi set-up. So far it has been cost effective for me if you can share one motor with multiple attachments. Downside, is if the motor breaks any investment in changeable attachments is rendered useless until you replace the motor - hoping that the motor won't fail again!
Also saves storage space and less general maintenance, especially if the individual tools would only used once or twice per year and then in storage until next season.