Mechs used to be the cloud chasers de-facto for sub-Ohming, they are basically a shell with a battery and a on and off switch. If you don't use a proper coil or battery, or do any bad mistake, they can be dangerous. The stories about e-cigarettes blowing, are almost always mech mods that shorted the battery.
Regulated mods have circuits, over small computer boards that controls the power, wattage, etc. and unless a fault, are very safe. Thanks to advances in the technology, most newer reg. mods can do everything a mech can do. Size wise, many are not much bigger than the mech mods now.
A good reg. mod with temp. control and sub-ohm capacity can be a wonderful device.
More and more mech mods users are switching now, while most mech mods users that stick with it just do it because they feel that they have "more manual control" over the way it's built, but they also tend to be people that consider it a very serious hobby and enjoy it, including (and mostly) the building of their coils and such.