I actually got a reply from YTV! I asked them three specifying questions, and they answered them all. So the new and updated technical information is:
– The “use once cards” are in fact the lowest of the low, MIFARE Ultralight. No crypto, no brains, no nothing.
– The normal cards are DESfire (first generation), not EV1.
– The encryption method used is 3DES.
I wasn’t expecting a reply, but i got one, and pretty quickly too! So thanks YTV.