In reply to Alasdair Fulton:
I don't have an Omnifuel but I do have a Dragonfly where I always use Unleadded.
For me there have never been any issues of clogging after a weeks service on the hills provided that the fuel is new and not been stored in the shed for months on end.
Hopefully the same will happen for your Primus.
The reason I've never bought Coleman's Fuel is the cost. Colemans is about £12 per liter and unleadded £1.