Neither of these brands (miniuno included) have the best safety reputation. Out of the three, I'd probably go for the Miniuno, because it can be fitted with isofix and top tether which is more protective than seatbelt fitting for this type of seat as long as the tether is used. If the seat is to be seatbelt fitted, the Kinderkraft would be better because the head wings look better made.
Only the Nania has had a crash test from ADAC. It doesn't do AS badly as some of the other cheaper models, but it still doesn't do great - crash test is here:
The score was 3/5 stars for safety (which correlates to "OK") however bear in mind that this test took place in 2012, the test criteria have been updated twice since then. If it was retested today, it would probably get a lower score e.g. 2/5 (just-about-passing). It is difficult to directly compare older and current scores. As a rule of thumb, though, older seats won't benefit from the safety advances which newer ones do and this is also a budget brand where they use minimal materials and prioritise cost over safety features.
The older (non-i-size) Kinderkraft Comfort Up got a poor result on ADAC but this can be ignored since this is a totally different seat, just with a similar name.
Kinderkraft and Miniuno are also budget brands but because these models are newer, at least you get more up to date safety, even though still not as advanced as more premium and/or safety-conscious brands.
It's difficult to buy a good car seat around the £60 price point.
Halfords Impala is £60 and is rear facing up to 105cm, though I have no idea if it's any good.
Cozy n Safe Fuji i-size is similar to the Kinderkraft seat, but has a more secure/universal belt path for fitting.
I don't love either option but they are probably the best you'll get for £60.
If you go up to £80-ish you have a few more options.
Joie Elevate R129 is a belt fitted option which is similar to the Kinderkraft.
Puggle Safe Fit & Gro is a top tether and isofix seat with an extended harness.
Halfords isofix Group 123 has isofix/top tether.
Kinderkraft Safety Fix 2 i-size has isofix/top tether.
Safety 1st Everfix has isofix/top tether and is made by Dorel (Maxi-Cosi manufacturer).
If you can say what age/weight your child is then we might be able to give more suggestions. Sometimes it is beneficial to stay within the one weight class rather than spanning multiple.