The most recent blog post talks about this.
https://www.mrmoneymustache.com/2021/01/29/margin-loan-ibkr-review/
Wow! What a coincidence. MMM and I were learning about these loans at the same time.
I credit MMM for giving me the idea to get a home equity line of credit in the past to buy another house. But this time, we both did this together (but separately ;-) ).
I did look up margin lines of credit after learning about this, but I thought it was only to buy stock with.
In the loan offered to me, I can do anything I want with it. And as my investments grow, I will have more I can draw from.
They were going to structure it as a fixed payment paying down principal and interest over 30 years, but I told them I preferred an interest only line of credit. I can choose to pay or not pay down principal on my terms, not theirs.
Honestly, as a single person with no dependents, I see no real need to leave anyone anything when I die. I figure I can keep this line of credit open and only pay interest (as long as it continues to make sense). If I die tomorrow, my siblings can just sell my investment assets to pay off the line of credit.
I do have most of my funds in Vanguard. If they offer a similar product in the future, I may just open a line of credit with them and just use it for an impulse purchase like MMM did.
I think some other banks use the term "asset backed loan" for this type of product.
I can tell you after handling my elderly father's finances, you don't want to get older with rising health costs and be house rich (mortgage paid off) and cash poor. And when you are older, no one is going to give you a home equity line of credit. We tried with him and he could only borrow a little.
This approach seems to solve those problems.