The ONLY rule about stirrups in the equitation is that black irons are not allowed. This nitpicky idea that equitation judges won’t watch you if your stirrups aren’t regular, heavy, normal irons with regular stirrup pads is fabricated by riders who don’t understand why they weren’t given a ribbon. You MIGHT run into an old school judge that cares but they will very rarely totally kill you for it. To be totally honest, it doesn’t matter unless you’re in a 3’6" medal flat class. MAYBE if you’re flatting a 3’ class that got very competitive.
You don’t want something that looks crazy, but I wouldn’t hesitate to use this type of offset iron http://www.doversaddlery.com/mdc-ultimate-stirrup®-irons/p/X1-07014/. Different stirrup pads, wide track irons, and (attractive) lightweight irons are all 100% totally fine. Jointed irons are a grey area, but if you want them get a pair with grey rubber and go for it. I would only switch them out for equitation finals involving a flat if you’re worried, but if you can find any USEF Talent Search finals flat pictures MULTIPLE well known riders who relieved good scores flatted with jointed irons.