Just updated three M4 SSDs to 070H in my 2010 MacBook Pro.
All went smoothly.
One of the three is normally in my other MBP (early 2011), and the other is normally an external. I do all the updating in the 2010 because I have to refit the internal superdrive to do the update, and so only want to do this on one machine.
Both MBPs seem to be running fine, as they were before (on all prevuius versions of firmware).
FWIW The 512M4 SSDs in both my MBPs are part of home brew Fusion Drives, which seem to have been unaffected by the firmware update.
Although I have got pretty quick at refitting my optical superdrive to update the firmware (five times now) I would love to be able to boot from a USB stick, if anyone knows how to do this on an older (ie supplied with a superdrive generation) Mac.