It depends on what kind of work is in demand in their market.
If the work is there, it's very worthwhile to have. The other end of the stick, is very ugly.
If they get metallic, and then realise they have no need for it, it's a painful mistake to make. There is a LARGE tradeoff in print speed between double CMYK and metallic setup. It's not a decision which should be made lightly.
Also advise your friend to keep in mind, that although it's possible to switch the machine from a metallic to a CMYK later on if required, it is extremely expensive. To get an accurate price, get them to check with their dealer about how much it costs for a complete conversion from metallic to CMYK.
I'm not saying it's not worth it, it's just a business decision which needs serious consideration and research. Like I said, if there is demand for it (or your friend is capable of creating/generating that demand), it's very worthwhile.
For the record, I went with the double CMYK setup and am glad I did, because it's exactly what I needed.