Kinderkraft car seats are made by Nania, which is a company who make budget car seats. Often this means that they've only gone through basic testing - completely passable of course but if you're concerned about safety (which I think you are because you're posting about it) the personally I wouldn't as honestly in a bad crash the seats won't do much. Similarly I wouldn't buy the Disney one. If you are budget conscious you'd be better off getting a good quality car seat and then you're buggy secondhand.
I assume, but could be wrong, that you're trying to be mindful of cost which is how you've come across these seats, in which case I'd suggest a "combination car seat" which goes from birth to 18kg. It will last you longer and save you from having to buy so many seats in the long term. Something along the lines of Joie should be less costly but safer. As a PP says it's safer to keep children rear facing for longer so one of these seats would work well.
We have a couple of the Britax seats for two of our children but not the one that you mention. They've been great. One was reviewed as a top choice on "Which" the year we got it and the other was recommended and fitted by a car seat safety centre. That won't mean that all Britax seats are great, but my experience of the "brand" has been good.
Personally when it comes to car seats I would look on the Which website at reviews. I usually sign up for the £1 trial and then cancel. It's very helpful and will give you more detail about good and bad car seats. Similarly if you have a company who specialise in selling car seats then I'd pay them a visit - they take account of car type, needs and budget, although you usually need to make an appointment.
