Sky RC offers a 5 in 1 card with a PPM which I have used to compare frame rates of several systems in the past:
https://www.aliexpress.us/item/3256802923192804.html

I recall having to do some conversions to get the readings into Hz and can't find the thread where I posted my results, but I recall comparing Fly Sky with Radiopost and KO Propo systems that I had at the time. I found it interesting to see the knock off Rx's where about 25% slower frame rates. Various models of Rx's from the same brand also differed in frame rates too!

*** I found the link to my PPM thread but it was on RCFiles which was retired a couple years ago