Are these addresses just for one time use or can I use them normally just like I use my Legacy address?
You can reuse segwit addresses an infinite amount of times, just like legacy addresses (im talking about in general, not about this specific website hich im not even going to click) , but please, do not put your private key on that website or on any website ever, ideally never export your private key, your wallet software should never show your private key. To move your founds from one wallet to another, then just send yourself the coins from one address to another.