automotive heaters

Hi all. Well, it is most definitely that time of year again..... cold time! It's below zero out there so I know winter is here. I was just
wondering, for those who don't have factory installed block heaters, what options are available, what are the pros and cons of them? Looking for both general information and perhaps specific to a late model Z28.
And uh in case I don't get a chance again before hand:
A very merry Christmas and happy new year to you all! And a happy holiday season to those who don't celebrate Christmas.
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