Same thing, just different names.
The reason they're not more popular is the wide bid-offer spreads which makes them far more expensive to trade that say CDFs. But the bid-offer spread would become a lot cheaper if more people traded them but as nobody is going to start trading them until others do it becomes almost an impossibility to get them off the ground.
In effect you tell me the reason you're not trading them is because I'm not trading them, and I tell you the reason I'm not trading them is because you're not trading them, so we both stick to CFDs.
The US doesn't have CFDs so maybe that's why there is more volume over the pond.
