These systems are the most frustrating to me, because it is the unusual transactions that are more important than the usual ones.
If I have eggs delivered every week, and one of those transaction fails, who cares?
If I buy a plane ticket for a flight that leaves in 30 minutes because of an emergency, I will be fucking enraged if that transaction is blocked.
Similarly if I can't pay the hotel at check-out and because of this delay I miss my flight.
Or when I arrive in a new country and can't pay for the taxi ride, and the ATMs don't work either.
All these events have happened to me.
Effective at preventing fraud - sure
But what about false positives?
If the question is whether you'll have any - of course you will! You will no matter what method you go with. At scale it's a pretty easy curve to optimize revenue on top of though, and you have to be willing to accept that bit. You know your customer LTV, you know your fraud rate/cost.
Sift gives you direct control of expected false positive rate, Radar hides that optimization under the hood I think?
At a previous employer we found both of those products to be effective.