Besides RV's my second favorite experimental in the Sonerai. Mine was VW powered but several have the UL-260 installed in New Zealand by Richmond Racing. They posted detailed engine performance numbers and comparison costs of ownership over 500 hours vs the Jabiru 2200 and venerable VW. The UL was considerably more expensive across the board initially, but was a much more modern and reliable powerplant over time.
Like anything, the more they build and put into use, the more reliable they become and the cost goes down. Unfortunately, in sport aircraft, those numbers are much smaller than in autos, boats or motorcycles.
I would love to have one in my Sonerai or a very light RV3 or Panther but the engine cost is three times
UL260 Sonerai outrunning a turbo Suzuki T-51. Quiet and smooth....