We were given a couple of Powerflares to trial, so far they have worked very well. They are extremely bright and the adjustable flash pattern is pretty cool. You can just chuck them out of the appliance if you want to mark a gate or entrance without any fear of damaging them. They also roll for miles if you get bored at MVA's
I'm not sure on the price but they work fine for us, I would say a combination of Eflares and the Powerflares would be ideal, if I could only have one I'm not sure - it is 50/50. The Eflares are good because you can clip them on things (road cones, people etc) but the Powerflares are good because I reckon they would be pretty much indestructible, apparently you can drive over them with a truck without any damage.
Probably didn't answer your question but I don't think you would be disappointed with the Powerflares, let us know what the prices are - that might help make a decision.