It really boils down to speed when you're going to compare Private Leech vs Public Leech.
If the Private can clear through both parts in under 2 minutes (maybe 1 minute 30 seconds) solo, than it would be worth it. If the Public can clear it really fast, you'd probably want to go with that.
When I use to do Expert solo, it would take me about 5 minutes maximum to clear out both parts. With a party, that time was reduced to practically half that time. The EXP gain was just as fast too so I didn't have to worry as much.