Software engineer here, so pardon a geek moment. The problem is trying to find one that will always-and-forever work reliably with both iOS and Android. You really need to pick a priority, or if you desperately need both platforms, buy two readers, one for each. They weigh almost nothing...
The reason is the communications protocols are different on the two devices. These card readers have SUPER simple "brains" and expecting them to support every host device's protocol oddities is just asking for trouble. Best to pick one that's known to be reliable with the platform you care about.
This is what I use for Android:
https://www.amazon.com/gp/product/B01JJ1VDQK/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
I'm not endorsing it, just sharing it. So far on a Nexus 6P I've had it for 2 years and must have viewed hundreds of photos with it. Works every time. I use it to read cards from a nice Browning trail cam and two not-nice-wicked-cheap garbage ones I put in places where I think theft might be a risk.