I've just realized, that másmovil have discontinued their monthly flatrate for € 20. Now they only offer data packs of 1 GB (€ 14.90/month) and 300 MB (€ 5/month) with exceeding traffic being charged with € 0.03/MB for both tariffs (see:
Total movilidad y ahorro con la tarifa modem USB internet movil).
Their customer care is also disastrous. Having sent all registration information including my scanned password 3 days ago to
datos@masmovil.es, my SIM has still not been activated yet and after calling customer care yesterday and today I was promised callbacks from an English speaking operator twice, which I haven't received yet either.
It took me days to find a másmovil SIM during my last vacation at Gran Canaria and now before I got to use it prices have increased dramatically and I can't even activate the SIM card. Perhaps prices will come down again after the holiday season.