I used mycashless at two different events, and both times it was a horrible experience.
mycashless was either extremely slow, making lines move much slower than the lines using other payment methods, or it became useless because there was no signal at the event to add money to mycashless .
This creates a situation where you can lose access to the money you added. If you do not have enough balance to pay for something, you cannot combine two payment methods at a festival. Then if there is no service to top up mycashless , the money already loaded becomes useless and you are forced to go figure out another payment method anyway, such as getting the bracelet or whatever else is available.
mycashless says you can request a refund, but that was another problem. It allowed me to add money using an American bank account, but when I tried to request a refund for the unused balance, it would only allow a refund to a Mexican bank account because the event was in Mexico.
My recommendation is simple. Do not waste your time or your money. Use the other payment methods available at the event instead.