We eventually will charge a monthly fee as described in our Form CRS, but we are waiving this fee for the time being. Eventually we plan on making money like Robinhood, M1 and other commission free trading pioneers. This means PFOF, Stock Lending, line of credit and other potential revenue sources. We are not currently offering these products. Please see our website for more details and our disclosures: https://double.finance

What will be the structure of that upcoming monthly fee?

I'm not interested in investing my time and money getting onboarded with a service unless I know the long-term fees are going to be amenable. If it said something like, "$15/mo and free for the first year" I would be on board.

Typically an ETF takes a management fee of 0.1-0.5% of assets per year. I expect this build-your-own-ETF to do the same, with fees on the higher side.

They specifically say no AUM fee.

This can change on a whim and you have no security against it.

For example, Guideline. They charged fixed fees on employer 401k accounts , until they didn't earlier this year.