Haas has shown more in two races than either Caterham or HRT could achieve in eight seasons combined. They're much more competitive and assuming it's no longer possible to set up a proper team from scratch, then their model is the only credible approach to modern F1. Grid numbers are also important. That's why it's good for the sport.
But there's no doubt how dependant they are on Ferrari. If teams like Sauber or Manor suddenly go bankrupt, and all of the replacements only follow the Haas model, then the grid will become much more homogenous with cars that heavily derive from the top teams. Making grid numbers dependant on those top teams concentrates their power. This isn't necessarily sustainable and therefore bad for the sport.
I'm inclined to think it's good for F1 as things stand. Time will tell of course but right now and on balance, do you think the Haas quasi-customer car approach is good for F1?