Theres often little difference between some models, what you have to be careful of is the full model number as that tells you exactly what you are getting.
The basics of the unit are the same, ie 8 poe connections, interface, just subtle differences in what they can handle, so production wise at HIK Vision scale there maybe no difference or very little is less than a few pounds, don't forget a manufacture makes for x and sells at Y, a distributor then buys at Y and sells at Z, if you then get a retailer involved they buy at Z and sell at A, so any differences can be magnified a little by the time it gets to the actual user.
so K and I models are 8MP and 12MP capability the 2 indicates they can take 2 hard drives.