Based on what I know, they made a huge mistake. Unity is a solid engine, with a lot of support, and is very flexible. You can choose from 5-6 different languages and scripting languages to do the code with and you can mix and match, and not have to stick with one language. Unity has a much more powerful and update rendering engine. It has a very extensive shader library. It has also been used in many published titles.
Hero, has very dated graphics, your options for expansion and improvement are limited, you have to learn their scripting language to do anything. The shadows are terrible and trying to improve anything causes a very bad performance drop. Hero is used by people, who want to throw together their own backyard MMO and sucker people into paying to play it before it finally goes under and disappears. It is a turnkey package that handles networking, billing, etc, and is terrible at anything else.
Those of you, who invested money into this game, I urge you to contact the devs immediately and petition to get back onto the Unity engine. You invested in a Unity game, not this Hero crap.
Is it a good move? It is for them, so why wouldn't they promote it? It is for someone, who wants a cheap-ass engine to toss something together that already includes billing, so they can all get paid and sail away into the sunset never to be heard from again, with all of your money and investments.
I may sound dramatic, but it has happened many times.