On Monday, February 19, 2018 at 11:26:53 PM UTC+3, Dave Springford wrote:

"Slippery, difficult" is concept invented by old men taught in primary gliders. No student even understands what that mean if only thing he/she flies is Duo.

That still does not mean the student will be able to solo in a Duo in the same number of flights as they can in a K-21.

I'd be very surprised if there is any significant difference in flights to solo between an ASK21, a Grob, and a DG1000 with 18m tips.

The Duo might be a little bit more. But probably less than soloing in an ASK21 and then converting.