Great idea and solid list. Please note that a ponzi IS betting and whatever money you put in, you must expect to lose. Never invest more than you can lose.
I've already write something about the risk in the first paragraph of the thread:
Note that all the sites linked below have high risk, do not invest more than you are able to lose!
Maybe add another risk-level. Coinsdouble paid me, but I hear multiple stories about guys who they didn't pay. High-risk.
Add the risk-level is a good idea but how can we decide equally the risk level?
Extra risk? Extra means more than normal, so you instantly show there is a risk already.