I believe it was "RC Reports" magazine that did a review of the two engines and they found it strange that Horizon would offer both engines when the trainer system engine made more power and was a little more user friendly. Do a little research and you may find the article.
The EVO engines that I have actually used ran just fine and had no problems other than they needed a long 4 stroke type glow plug sometimes to make the best power. From the recent adds it seems the photos of the newer versions have a more upright glow plug.
Fred