I have one each of the U-Key 15, 35 and 40 variants from the original JJ production efforts.
Please note the 15 is no longer offered but flies well on a FP 15 or Norvel BigMig 15 (they are interchangeable).
Shown here (L-R) are the 40, 35 and 15. Span is about the same on each but each larger size has increased chord (lower aspect ratio).
We power the 15 with a Norvel BigMig 15, the 35 has a Fox 35 and the 40 uses an FP 25.
Airfoil is relatively thin so they do fly a bit fast but are very smooth and stable. My son reports the U-Key 40 flies much like his Sig Primary Force ARF for about half the price.
If you can tolerate ugly, you'll get a lot of flying value from the U-Keys. We still fly ours quite a bit. Our 40 ship was accidentally built with some dihedral in it but still flies well.