I have a Sandisk 64GB Class 10, perfect for content on my M9.

http://www.amazon.com/SanDisk-Memory-Adapter--SDSDQUAN-064G-G4A-Version/dp/B00M55C1I2/ref=sr_1_2?ie=UTF8&qid=1428953593&sr=8-2&keywords=sandisk+micro+sd

Works really well for me.

A comparable sandisk is fine too.

yup, this is what I use:

http://www.amazon.com/SanDisk-Ultra-UHI-I-Class-Memory/dp/B00M55C1I2/ref=sr_1_2?s=pc&ie=UTF8&qid=1422397796&sr=1-2&keywords=sandisk+micro+sd

each score 4.7/5.0 in reviews (with thousands of reviews), I just picked the one that happened to be cheaper at the time

I used this in my Galaxy S3 and have been using it problem free in my G3.

SanDisk Ultra UHI-I/Class 10 Micro SDXC Memory Card, 64GB https://www.amazon.com/dp/B00M55C1I2/ref=cm_sw_r_awd_3ybYub0P07XWE

OK, sweet. Do you know if the SanDisk UHS-1 cards work?

I have a GoPro 4 Silver. Can I get away with SanDisk's Ultra or is it worth spending more for the Extreme?

They're all "good luck" up to about 8Gb, then the reality hits and by that time, it's too late to return it and all of your data is gone.

Check out this one. Looks real, right? Wrong.