I bought a 1st gen Nabi a year and a half ago. What you're getting with a Nabi is a tablet that you can give to just about any child and not worry about them screwing it up by accident or installing a bunch of apps without your permission. You get an interface that only allows the child to use the apps you specify for them and doesn't let them get into the settings to make unapproved edits. It does this very well. I've found the sideloading very easy.
The Nabi does have a known issue with the charge port but you can charge it with the usb port just like any other usb charged phone or tablet so that's really not an issue. Pretty much every family I know has a stack of usb chargers sitting around already from all the phones and tablets and such they've bought over the last 4 years anyway.
I've not had any issue with using an SD card. I think it is limited to 32GB but I think that's pretty standard for most tablets out there right now. I have ripped a dozen or so movies from DVD's for my son to use in the van while traveling. Its nice to not have to worry about him scratching DVD's.
And the mommy/daddy mode on the Nabi turns it into a regular fully functioning Android tablet if you want to borrow it for a bit.
I find it interesting that people complain about there not being enough free stuff for the Nabi when there's even less free stuff for other non-Nabi tablets. *shrug* The Nabi does come with a couple dozen free little apps and it can access all the same free stuff that all other Android tablets can access, providing it runs on Android 4.0 (which is what the Nabi 2 runs on). The Nabi Jr. and Nabi XD are both on Android 4.1.
If you're buying a tablet for a kid and you want easy to use parental controls, a Nabi is an excellent choice.
If you're looking for the best bang for your buck for a slightly older kid or for yourself in the 7 inch tablet arena, then the Samsung Galaxy Tab 2 7" is probably going to be your best bet. It has received excellent support from Samsung regarding Android updates and has some great specs. I bought two last year from Walmart refurb'd for $140 ea. for my older two kids. They have put COUNTLESS hours on those things and we haven't had so much as a single hiccup.
It does bring free software, but when most of it is for games/other content that my kid doesn't want then I can't really do much with it.
As for the charging, yes I tried charging it on my laptop and it didn't work. Maybe I have a defective unit, between that and the SD card issues.
Yes, a closed system is great for a little one, but when I have to side load an app store to get something as simple as Angry Birds Star Wars.....We have a Note 2 7"as well, plus many other Android devices, and there's usually a lag between something available on Google Play getting on Amazon's app store. Lags are not good when the 4 y.o. sees his sister playing a game he wants.
Anyway, I hear that they're now doing Disney & Nick versions so maybe the content will improve.
It would be interesting to see about that "kids Samsung note" that was mentioned earlier