it all depends on the threading you get for the ego style batt. most are just standard 510 female connections
a kgo is just another model of an ego battery. can't say i have personal experience with them but most if not all will be the same in shape and have similar insides. they're also differences in how much power is regulated from ego to ego. but it's not much of a huge difference imo. this will just depend on your attomizer/cartomizer/clearo-whatever ohms.
some have five-click protection which is great to have as a feature if you want to put your ego in your pocket. they're variations of that "five-click" with some having 3 click protection and others having a form of a 10 second cut off (in which you then have to connect to the charger or click it 5/3 times to turn it on again). the only ego with a major difference on the inside is the ego-c twist. which is what i'm going to get to attempt to go back to a tank system later this month. cheap vv ego.
it's also a bit longer then a standard ego.
i'm going to actually go ahead and get it from Joyetech.com, as i want to have a legit (revision?) version of an unbranded ego-c twist.
also to answer your question, you have to think of this hobby, like computers. more-so computer hardware. so many brands and companies out there that produce similar stuff that do similar things, price them at different prices, but at the end of the day it's only worth it if your satisfied. you can get a really expensive product, show it off; have un-needed bells and whistles in it, and vape on it all day OR you can get a relatively cheaper version that has the same core qualities as that expensive version with out the flashy "overclocking" features (variable voltage). as such, you can go with a very well known and good rated vendor, or go with something you can probably find on ebay that has a bunch of little golden made in china stickers all over it.
and as with PC's, you can reuse your old equipment on your new set if it's capable. just my
Buddahbelly, I was going to chime in, but you really have gotten the basics right here already. Doneee, that was an excellent comparison! I like tanks, but just use them at home, really.
Bottom-feeders are also very good, for being away for a while, and not worrying about carrying extra juice. Most all of them will easily hold a day's worth. Vmods are good, but I have two friends with them and say they can leak.
which version of the vmod do they have?
i've yet to make mine leak at all. I've purposely tried my best to make it leak. I bring it everywhere. i run with it, i play games with it, i go everywhere with it. and i mean everywhere. i can shake it all up and over fill it. no juice at all will go outside into the "catch cup" or leak within the mod itself. i've had 100% PG, 70/30, and 100% vg (as of now) and no leaks. the only way i can see it leaking if i had the old gen vmod with crappy seals for it.
sorry for the off-topic-ness, but i must defend my love.

since i got a hold of the vmod, i figured i wasted a lot of money getting different tanks just for changing up flavors. it works best for me on my vigorous change of paces and flavors throughout the week.