For the benefit of those that are considering getting a mandarin I have attached the wetwebmedia site here. Make your own decision.
http://wetwebmedia.com/mandarins.htm
Paddy your post mentions nothing about compatibility. You simply asked for advice on whether you should get one or not.
If you are adding a refuge and cultivating pods for your 70 gallon than food should not be an issue.
I would be concerned that a docile fish like the mandarin will become a victim to aggressive fish like the six line wrasse but I do not have both so can't help you with your decision.