I have to say I find this quite amusing.
MCT is the maximum thrust certified for continuous use. There is not certification problem with its use, there is however a ware issue, as there is with all engine use.
Airbus has its advice spot on in my opinion. Use it only for safe flight. If it's not required for safe flight, then why are you using it? However, "safe flight" is open to interpretation. Would safe flight mean meeting an ATC restriction? How about if not meeting that ATC restriction would take you outside controlled airspace?
So my advice is to use it if you feel you need it, but use it sparingly. It has a cost, but doesn't everything!