I have used one of the sitting Harris bipods (approx 12"-24"). Harris makes great quality products, but I did have a few issues in the practicality of use.
1) Leg adjustment. The one I used had the friction locks. It just took a little time to adjust both legs on uneven ground. Leg notches wouldn't have made it any better, only harder to adjust. Leg notches for a benched bipod would work well.
2) Swivel is really more of a "cant". It definitely helps make adjustment quicker since it is a user adjustment that isn't changing the length of the legs to get the crosshairs vertical.
3) Groups. Tall, sitting bipods aren't rock solid.There is a lot of wiggle, even with all the hardware tight. Plenty solid for big game hunting, but IMHO a solid rest would be better for varmints.
4) "Huntability". When you finally have it all set up the way you want it for a certain shooting window, the game has to come from the other direction of course. There's no time to adjust on the legs. It's a matter of sliding around and usually balancing on one of the bipod legs to get into a workable shooting position because the uneven ground is different at the new location.
I like Harris bipods - they are well made and relatively light, but IMHO, from a sitting position, they are a little clumsy and may not be able to be solid enough at full height to attain the accuracy necessary for varmint hunting.