They are good fun, but IMO it is better to sped your money on 2 girls at different times or a longer session with the 1 girl, as you can not fuck them both at the same time.
Also a lot of condom changing between going from 1 to the other,
Whilst it is exhilarating, and worth ticking off the bucket list, I would not go for MFF again, as would rather have more time with just 1.