i have been using the D-2 Olt calls since the 60's. i have used the cutdown keyhole D-2, the regular keyhole D-2, and the round hole D-2. there is a VERY small difference in the sound of the three calls. They are all very ducky sounding calls...incredible for soft calling and feeder chuckle. the cutdown keyhole is a little more raspy and mine did not have the volume capability of the other two. regarding value, the olt company is no longer in business but there are so many for sale on ebay (alot of them still new in the package) that somebody must still be producing them. the keyhole D-2 calls sell for $25-$45 on ebay(dependinbg on condition)...more if they are new in the box. i sold my keyhole call and my cutdown version keyhole on ebay last year. i use my regular round hole D-2 every time out. i don't recall what i got for my 2 calls, but they were well used. the Olt D-2 was produced for over 60 years, making it the largest selling call in the history of duck calls. i am a hunter, not a collector, so i only keep the stuff that seems to work in the field for me. there may be some collectors that have more info. the ebay handle for jim olt (former president) is oltdaddy. also, former olt employee, dave jackson, has started a company in illinois making a few clones of the olt calls..i think the company is called DJ's Illinois River Calls (not sure of the company name though).