I believe there are various different qualities of smoke. You can get cheap mass produced smoke from China, even 'fake' smoke from China would you believe. This smoke can be a little volotile, a bit like IB cells
You obiously pay more for higher quality European produced smoke, as it is injected into the components using really big cool looking machines (like the pie making one in Chicken run) which cost money. In china some little guy uses a sqringe.
You also have to treat the smoke with respect, don't try to use all its power to quickly (Star-Trek, 'she will no take any more captain' style), which is perhaps where some speedo manufacturers are going wrong. They should probably use more smoke, or higher quality smoke. But this would put the price up I'm affraid.
G