I'm not an SD card expert, but this is the little I do know...

The FreeFallFilms system will work with any card that the mac can read & write, so the key point is buying cards that work reliably with the GoPro (or other camera).

The camera needs to write a lot of data fast, and it has to operate in very low temperatures.

Brand
There are definitely less reliable brands out there.
Between slow cards, and bad brands - people definitely have freezing problems where the GoPro just shuts off.

I don't know enough to navigate between them, so I'd say stick to a well known brand.
SanDisk is the only one I really recognise...

Size

They don't need to be particularly big. A jump is typically 2-3gb.

Ideally, you're only putting one jump on a card.

In practice, the cheapest cards are mostly 64gb which is more than enough.

Speed
Speed really matters. For write speed, it has to be fast enough for the GoPro.

GoPro requires microSD card with v30 or UHS-3 rating

This site has a good chart on the multitude of speed indicators

In terms of read speed - faster reading cards will be much nicer to use.
Waiting for the files to copy is a significant chunk of the time to process a video!

Result

As of Aug 2024 - this looks like about the best deal to me

San Disk Extreme £8.5
64gb, V30 UHS-3, and up to 190MB/s read speed.
This is about the same as any slower or smaller card from SanDisk that I can find.

or for a little more
San Disk Extreme Pro £11
64gb, V30 UHS-3, and up to 200MB/s read speed.

I'm honestly not clear about extreme vs extreme pro - but it says it reads slightly faster...

You can definitely save money with multi-packs from different brands. That seems like a bit of a risk though...