Are there any risks to doing this? Using moneybox

My partner 31m and I 25f have almost 3k in savings, we are both from the uk and have been married for a year now and known one another for slighly over a year before getting married.

We are both using natwest bank and have a joint account. I contribute mostly and he contributes when he can, he pays all the household bills and does earn more than me.

He created an account with money box and told me that we should move our savings there to get a bonus from the government and then he will move it back into our account when we are ready to buy our first home. Unfortunately you cannot create a joint account using money box, are there any risks to doing this? I didn't really trust the idea and he said i can do it instead if I want because you just can't add another person's name to it. Once we have a good amount atleast 80k he will move it back to our natwest joint savings. I can do that for our second home he suggested.