The only issue I have had with Robinhood is regarding tax planning, because they only support FIFO sell orders. There have been several instances where I would have preferred to sell shares purchased more recently, so that my older shares can pass the one year threshold for long term capital gains. The ability to specify lots when selling shares would be worth money to me.
The best way to create reusable formulas in your workbooks is to add your table to the data model (which creates an in-memory tabular cube) and write measures using the DAX formula language. This has the added benefit that a single formula can be written to aggregate data at different levels, for example, a sum can be calculated over days, months, or years. This will only allow you to share formulas in a single workbook. The data model in Excel is powerful and under utilized.