Been about 6 months with an SD card and a good quality reader plugged in. Only issue so far is if you fast forward to the beginning it will slip back to the start of the 90 minutes.
Might try the extension cable to see if it's flawless but I'm satisfied with how it works now.
I made sure to get my sd card and reader from Best Buy as Amazon has too many counterfeits.
On a separate note, if it's possible to record live tv with just a flash drive like this, why isn't there a similarly simple diy DVR solution?