I've looked at investing in a Freestanding several times and concluded it's not worth it. There is a big difference from being a founding member who owns a big share in one ED or company, and being an investor in an existing company.
The market is quite saturated, so most of the new ones opening are by already established companies looking for investors.
When you invest in a freestanding, you are giving money and time. Typically about $100K buy-in to purchase "shares". Each share is about 1% ownership of the company at that site. You also have to work one 24 hour shift per share that you buy. Most physicians purchase 6 shares which means they have to work six 24 hour shifts in a month. The initial startup pay is low, around $100/hour to work those shifts.
Working six shifts may not sound hard, but effectively it puts you out of commission for 12 days in the month. Those six shifts would give you around $15,000 in income for the month. If I worked at my regular job instead, I would work eight 12-hour shifts which at a conservative $300/hour would give me $28,000. Over 1 year that is loss of $156,000 in revenue for me. The average Freestanding takes up to 2 years to start generating profit. The means the total buy-in at that point is $412,000. Even if the ED starts making a profit of $3 million per year, the 6% share would only equate to $180,000. That means it would take a long time to make up the amount of money lost to the buy-in with significant risk attached.
I know several colleagues who have been essentially scammed by companies. They did their buy-in, and when the facilities started seeing enough patients to make money, they didn't get their share of the profit. The excuse the company gave was that they were "re-investing" the profits into expanding to other sites. Litigation is pending.