I've owned and built both - a Unique 427 and ERA 427.
After studying both and going down this path back in the mid 90s, the entire time I owned my Unique, the goal was to make it as close to as an ERA as I could on the outside and underneath the body. The day sort of came true when ERA accidentally posted a pic of my Black Unique 427 from a group photo shoot, and had it on their website. It was pictured there for over a year and I finally called them up to break the news to let them know the car was not an ERA, reassuring them it was a Unique
. It took a lot of "extra" work and subtle changes all over the car to fool ERA. Hehehe. After having it all done and enjoying it for four great years, I reluctantly sold the Unique, decided later to try the ERA next. The cars are designed and built in different ways, look different, drive different, feel different, handle different. If you are not a detail oriented person, none of this really matters for comparison purposes. It all comes down to details and what you like best for the cost.
You can put as much $ into a Unique to make it look like an ERA. Functionally, they are different driving and feeling cars being super critical. If it were me, I would figure out how to ride in and drive both, and determine what your true budget and real desire is for either car. Good luck on the journey.