It's a nicotine salt so it's stronger but less harsh on your throught. A 50mgml nicotine salt concentration ends up being as 'strong' as ~28mg/ml nicotine freebase (since the salt makes up ~45% of the molar weight) but has the throat hit of like a 12mg/ml nicotine freebase.
The volume held in the device & volume per 'puff' is also a lot less hence the smaller devices.