What kind of iPad should I purchase?

Things to consider:

Takedown's minimum system requirements.
Cost. Suitable used iPads are often available for $200. New, premium iPads can cost more than $1,000.
Physical size. An iPad Mini is easier to lug around a tournament than an enormous iPad Pro.
Storage. More on-device storage is better for video recording since you don't have to be as disciplined about moving the original videos off of your iPad to your preferred backup location. For scoring only, Takedown doesn't require much storage -- a 16 GB iPad will work fine. For video recording, suggest a minimum of 64 GB on-device storage.
Features. Recent iPads -- especially the iPad Pro line -- have more sophisticated sound and image recording.