It really boils down to the implementation. Also, you need community support. What really helped HHVM mature is that by using PHP for something large scale, the

It really boils down to the implementation. Also, you need community support. What really helped HHVM mature is that by using PHP for something large scale, they were able to see its shortcomings. Most other forks are not driven by that. As such, their upsides are questionable, or they just offer some performance boosts, that are achievable even without the trouble of forking.