A few important pieces of information first:

After completing the registration, you will be assigned to one primary club automatically. That can be either Ultimate Vienna or EÖFC - this is part of the symbiosis agreement that was made when both clubs created Echo & Rumble together.
This means that you will pay you main membership fee for either one of the clubs, and then a 30€ "Symbiosepauschale" to the other club. This makes you a full member of both clubs for the price of one membership.
That means you have to make two bank transfers to be a Echo/Rumble member, but other than the transfer recipient, everything else is the same for everybody.