Quick update — upon further examination of the CSV file, I do in fact see the logged data at the selected sampling rate buried deep in the file. What appears to be happening is that the meter is ALWAYS logging data to the SD card whenever it is inserted, regardless of whether logging is enabled or not. When logging is enabled and then disabled, a new log file is immediately opened. I also notice that the logging interval is not that accurate (e.g. 11.3 sec interval when 10 sec is selected). I am running firmware version 1447470000 on PCB 008 with iOS 9.3.1.
Still loving the meter — it is amazing what you were able to accomplish with such a wimpy CPU. Imagine if you had one of those sweet 32 bit ARM Core M4 bluetooth modules from Nordic ;-)