Nuclear pulse propulsion is certainly interesting, but it would face the same problems nuclear energy itself faces - it sounds scary and honestly would only be useful once in space for the most part because of it.
And to the other point, as far as I understand it, the point is not to provide more thrust than rockets, but to provide an alternative that can be used not only to reach orbit but also just to fly around the atmosphere with much lesser costs in terms of storage for the fuel.
Indeed. The concept of lifting up a megasized rocket directly from earth could work out in the 50s or 60s, but not today. Anyway, if we are to scale out space travels, I think we need to think beyond chemical rockets (explosive or conventional).