What iPad should I use?

More crucial than the specific iPad model is ensuring that your iPad has the capability to be upgraded to at least iOS 15. 

Limited functionality may be available on earlier iOS versions. However, please note that all app updates from the forthcoming version GymAware v5.0 will exclusively be compatible with iPads running iOS 15 or a later version.  

If you'd like to be recommended a few models that meet the criteria, you may consider this list from Apple.