I've used em for a couple years. Yup, using a leather glove is a good idea to avoid a sore hand. I think you need to be a fairly large person to push them in easily by hand. Using a corker to push them in is good otherwise (I do em by hand tho) ... yes a mallet is used by some to get them to seat if you have trouble doing it by hand. As far as sanitizing them, don't cook them ... just a soak in metabisulfite is fine.
Though they are being used by more and more larger commercial wineries, as I understand it the verdict is still out on their use when you are putting down wine to age for an extended time (not according to the manufacturer but according to folks who have been taking a "wait and see" approach). So, for grape wine being aged for 3 or 4 years plus, personally, I'd still be using natural corks. But I like zorks a lot, and as they are proven over the long haul I would switch to them in my wine put down for longer storage and aging. Zork SPK are the ones used for sparkling wine. While the SPK's are not suitable for hand corking, that system is available.
If you read a zork manual capping sheet for the STL (standard) zorks there is some extra "fitment" that is supposed to be done to insure that the zork has been installed correctly including the use of CO2 to chase the headspace in the bottle, none the less I have had good results so far using them to cork by hand at least in my wines expected to be drank sooner than about 3 years.