The small one or the "big" one = Firefly Q6 ... I tried both, even with >40g Firefly Q6 Tello flies :)
Look photos ... secure additional with rubber band ;-)
I wrote above "4K is intern pushed up"
Yes, that's right - I have 2 action cams (Yi 4k+ and SJ8 pro) with REAL 4K/60(!)fps, but they are to heavy for Tello.
Look above Firefly Q6, it's a cheap very good camera with 40g - more weight isn't okay for Tello
Hawkeye Firefly Q6 4K 1080P 60FPS HD Mini Camera for FPV Racer
Tello has no memory card, so all is stored in the smartphone.
No card - this is a little "big" disadvantage - but you can live with it.
Look youtube videos with small cameras 14-25g (with microSD) mounted on Tello
A little bit "bad" are 1280x720 videos - because there is no microSD card in Tello and videos
are tranferred via WiFi. 3.14159% better they are by using a WiFi extender. :-) - photos are okay.
Tello ist the best :-)
For half price you get Xiaomi Mitu, for 1/3 price Linxtech 1802 / Realacc R20.
All three have "bad video"- 1280x720, because NO microSD :-( Photos are okay.
Hmmm, with my ("fullhd") cams it's no problem, now I will try Firefly Q6 (42g, 4K - 2880x2160)
my test: Firefly Q6 as dashcam
https://youtu.be/SFeghMVklE8