We recommend using devices that are at least on iOS 10.
Most of the current Apple devices can still be used with SeriousMD. There are a lot of SeriousMD users using an iPad 2 and the first generation iPad mini.
You can upgrade the hardware later on if you see the need.
The main differences for the newer models are the speed, smoothness, the ability to process more data and the available memory.
For super users / heavy users with large amounts of data already (approx over 10k patients) we recommend the following iOS devices.
All iPad Pro models
iPad Air 2
iPad Mini 4
iPad 6th Generation (2018)
iPhone 8 & above