I have tried several of these single flute cutters and results vary relative to the quality. You can buy them in solid carbide from US$ 4 to US$ 60, in HSS from US$1 to US$ 10. This price is for a 6mm cutter.
As blackburn mark mentions, measure the exact diameter. Especially the cheaper ones vary slightly (some up to 0.1mm).
I can plunge even the cheap ones in aluminium at twice the speed than 2 flute milling cutters without any vibration. I have cut solid hardwood, MDF and acrylic with great results and performance in aluminium is even better. And it does not die if it takes a chunk out of your vice either. I use them on my router and my mill.

If you thought your router would be not solid enough to cut aluminium, give these a try. You could be up for a nice surprise.
On my home made router I cut 16mm MDF in one cut at 400mm/min @ 12000rpm.