Second the Gamut P20/P30 (depending on what ring you want to run). I use a P20 on my trail bike with a 32t ring.
Naturally they do have a lower idler guide but the drag is so minimal as to be hardly an issue. They are so simple to fit as well – literally I just bolted mine straight on within 20 minutes. Every other chain device I've tried to fit has been a **** ball ache of the first order.
I know you have ISCG tabs but if you really do only want a top guide, then the BB mounted 1.X MRP really is the best solution. I have used one albeit briefly and if I am perfectly honest, the only reason I went back to the Gamut is because it looked better. I know that sounds utterly ridiculous, but there you go; the MRP works fine for hardcore trail riding and I had no problems loosing the chain.