The design isn't fantastic - although it's still better than some, like the Heavy, Fast, Level, Lure, Luxury, and Repeat Balls - but I don't use the Master Ball much these days because I don't really need to...and I tend to save it just in case I do need it. Legendaries these days don't usually have an obscenely low catch rate like they used to (at least, I don't think they do...maybe I've been getting lucky?) but with things like roaming Legendaries I just cannot be bothered, so it's faster and easier to just throw the thing at them. I'm only out for dex completion anyway so it doesn't matter what I catch them in when I'll just box them and forget about it. xD