LSTM vs ARIMA for demand prediction
ARIMA models are basically linear models, so they can only work if the relation is linear (or linear integrated). They are easy to estimate.

LSTM can model more or less any relationship, but at the cost of additional computation and require more data to be trained.

So start with ARIMA if you don't know anything about our data, if it doesn't work, use a simple LSTM model and then complexity it to match what you need with the test set.