From a customer care point of view I think it is a very short sighted tactic. If I book to fly with a particular carrier I expect to get their level of customer care and safety in every respect.
Why exactly?
Food and drinks service on board will be the same as all other Monarch flights and they'll be a few Monarch cabin crew on board to ensure customer service levels are maintained. The only difference between flying on a Monarch aircraft and an Aurela one is the interior, which while it may be older, is probably just as comfortable.