I was just looking at them yesterday! I like the magnetic ones because I can just throw them on when I go skiing or someplace really cold instead of getting a Wolf that sticks on. I was doing some research over on the oil forum and there is a ton of threads, none of which were conclusive for block VS oil pan heaters. If you want to read through them you can go to Google advanced search and under site put in bobistheoilguy.com and for search terms put in oil heater, or engine heater, etc. I was surfing through them for about 2 hrs lastnight! Bottom line is they work if used correctly(dont turn them on 30 mins before hand after the car has been sitting out all night), but using a synthetic oil is one way to reduce the need for one.
HTH
