Does seedsigner have great functionality too? What can it do apart from signing transactions?
Discussion
Well, to me it did the same as a cold card no?
I don’t think so. Coldcard is packed with features. I can’t imagine a Seedsigner has all the same features
Look here on their website. https://coldcard.com 
MK4 also has NFC. So you can use it with Nunchuck Wallet on your phone. I’m not using it because it’s not properly air gapped anymore but you have the option in case you need it