Calling both of these institutions "marriage" leads to confusion. I would recommend to all the former (let's call it "Biblical marriage") but I would only advise women whom I love to avail themselves of the latter (let's call that "secular marriage").
I would add that the divorce courts are very much geared toward women, so men should avoid secular marriage at nearly all costs. If they do go that route, then definitely get a prenuptial agreement - but keep in mind that feminists on the bench in divorce court will disregard it if necessary to achieve the pro-woman result.
There's absolutely no reason for a man to enter into a secular marriage. Avoid, avoid, avoid.
We’re on the same page. I think one is marriage and the other is legal union. And the latter can also be defined as legally defined serial monogamy.
And when one enters into the latter with that understanding, prnupts may become more of a significant thing. Frankly, it is very much a legal version of “making an honest woman out of her”. There is nothing spiritual there, by definition.
FWIW, for tax reasons my wife and I seriously considered getting married, but never involving the state in it. That is, legally we would still be single people cohabitating. We both take the spiritual commitment VERY seriously, however.