Basically every religion has some hope of afterlife/reincarnation. So for non religious people this also kinda provides this hope. And if it doesnt work out it is just a expensive funeral. If your dead body is burned, frozen or buried doesnt really matter in this case.
I would rather do a one time payment because they sure wont get money from me when i am dead. So a one time payment must basically be big enough to generate enough interest/stock market returns to make it worth their while too keep the lights on forever. I dont see this with a 50€ Subscription. Maybe they would do it like an ETF Investment Account which signs you up for Cyro Preservation after reaching a certain size. The money would have to be withdrawable while being alive though.
Besides that, as far as I understand, cryonics is heavily dependent on effects of scale. My hope is that by the time I'm about to get frozen, enough people will be interested in it to make it economically viable long term.