also had both. See the show me your singlespeed thread for pics.
The inbred was a bit flexier around the bottom bracket but mine was getting on a bit by that point and also i am quite big so that probably didn’t help. the head and seat tube angles are slacker on the inbred so i feel that the simple climbs better. However the price of a simple frame is almost the same as most of a fully rigid inbred so as they say, you pays your money and you takes your choice. you wouldn’t be dissappointed with either IMO.