I'm in my late 30s and have met and know couples who use/d NFP for a decade+. No one I've spoken with has said it's a huge headache, though some have candidly admitted that the self-control factor is sometimes challenging (that aspect is going to vary by couple, of course).

I can't speak to your experience, and as you say you have irregular cycles. BOM can actually be quite simple for many couples, STM a little less so since it tracks more fertility signs.

Here's a more recent report on a German study:

http://humrep.oxfordjournals.org/content/22/5/1310.short

"The STM is a highly effective family planning method, provided the appropriate guidelines are consistently adhered to."