Built right and kept light it will be no different than a supercub... AOI is the single biggest difference between good flying cubs and lesser ones, and the difference can be astonishing, being hand made even pipers were all over the map. I would go over any prospects with a smart level.
Lots of folks built these with a fixed horizontal and a trim tab. For my opinion on this you can reference the bird dog thread...
I have flown with a few guys that have nice examples of Cubbys, If you didn't know they weren't a piper you wouldn't know it looking them over, but it all depends on the builder...
Lot's of Smith / TCOW / Back Country cubs out there, they are not Pipers either, I think they basically took what Wag had (in terms of a cub clone) and took it to a new level.
There is a guy here were I am in Iowa that has built some really nice examples, including a hot rodded O-290... I would probably want one from someone that has done a couple... and don't forget the level...
I would love to have an experimental cub, and if the price, and build was right, I would probably not shy away from a cubby. The only negative to buying one is that you will not be the builder, So I'm not to sure you can get the repairman certificate. That is a biggie for me in the experimental view...
YMMV
Take care, Rob