in fairness Roger Gewolb said " It is never a good idea to borrow money to buy shares unless one is a professional share trader. To do so in order to buy illiquid, unlisted shares in a relatively new company through a crowdfunding platform seems to us somewhat beyond the pale "
so both Tom , the journalist and Roger agree , Its not a great idea - and it has never been offered, Monzo have just said you can, just as you could borrow from any other bank with an overdraft to buy Monzo shares, but they all agree its not a great idea.
I can link you to several more when a lot of people have said the same if you want -