Opinions vary on using a stay on case or not. (You can find quite some opinions on that in earlier threads.)
Personally, I prefer having such a SOC on my scope. In my case, SOC’s from Kite. It is not cheap (still cheaper than the Swarovski SOC), but compared to the price of the scope, it is a limited amount of money for some added protection. I’m not sure if the SOC will add significant protection for the body against bumps etc., but at least it protects the outer lenses better when carrying the scope over long distances, travelling etc. (both in the car or e.g. walking through a area/path with many branches hanging over the path). Also compared to caps that could fall off easier, or maybe even get lost with regard to objective caps which are rarely tethered. (If walking at a spot where I’ll probably be setting up the scope more often, I do leave the SOC open sometimes, with the tethered ocular cap on and the solar shader extended to protect the lenses.)
But personally, there is also another reason why I like having the Kite SOC on my Swarovski ATX 65: it draws less attention… (I love the view through and handling of the scope, and the Kite SOC is neat enough, simple design, while more discrete/neutral. Don’t get me wrong: the ATX design is neat! Just drawing more attention of some people to the scope for being a Swarovski.)