I have used the inline heater before on a car I used to have... not on my pathy. They don't tend to last as long and I don't know why. It seems like after a couple of years the internals just wear out. I replaced the one on mine and pulled it apart out of curiosity and noted that the impeller had simply corroded a very little bit, just enough to impede turning. But while it worked, it was nice. A block heater just seems to last so very long, maybe because of its simple design.
Contrary to popular opinion, it does not superheat your coolant so that it's super hot when you get in. It does heat it up and cut down on the length of time to when you get into your vehicle in the morning. It might save you 2 minutes. If your heater is working properly, you'll have heat quick enough. An old mechanic friend steered me away from it years ago and got me to spend some extra time flushing my heater core at the firewall every fall. That has always made for nice heat pretty quickly.
The magnetic block-type heater in that bottom picture is great for heating the oil pan itself or the transmission in the ultra-cold climates of the north, but probably overkill for anyone else. I have a friend in Iqualuit where the average daytime temperature is -50 C... they need to use something like that if they turn off vehicles overnight.
My mechanic friend said the oil dipstick-type heater is more of a gimick than anything. Oh, and he was a heavy duty mechanic working in the oilfields... out in the bush... where they don't have garages... he was very cranky too.