I'm about a third of the way through this book and I just want to comment about the racism and bigotry presented so far.
Yes, the characters are racist (both the Americans and Pan-Asians) but I think it is important to take this in context. Not just with regard to the time this book was written but with regard to a central premise of the story.
After WWII, the cold war had begun but had continued to freeze well beyond the level it actually did historically. The Pan-Asian countries had maintained a strict isolation from the west and vise versa. This had become enshrined in law preventing any contact between the peoples of these countries for two generations. Knowledge of each other's culture, languages and religion became virtually non-existent and so this explains why the people (on both sides) had strong pre-conceptions and prejudices about the other side.
It comes across quite strongly that the racist sentiments expressed are only that of the characters and not of the author. Indeed, there was one character, an anarchist hobo, who sees the Pan-Asians as just people, induced to hate, kill and conquer by their state just as the Americans were themselves induced by their state. In the eyes of this character, it is the respective governments that were the real criminals, not the people themselves. And I feel that the views of this character are probably closer to the personal views of Heinlein than any of the others.
A quick word about the science in this story. It's a bit fanciful to say the least. According to general field theory, there are three types of forces: Electrical, Magnetic and Gravitic. The "Ledbetter" effect, utilised by the protagonists in thist story, involves tapping into the spectra (besides the electro-magnetic) that general field theory predicts should exist: electro-gravitic, gravitic-magnetic and the three-phase electro-magnetic-gravitic. I suppose field theory was quite new when this book was written but still, Heinlein's grip of it seems to be quite weak. Even with my very limited understanding of it.
This isn't really a negative for me at all. I have no problem suspending belief and just running with it but I imagine that for some people it may prove problematic.
At 140 pages, the story unfolds at a breakneck speed, never pausing for breath. The advantages of this is that you never get bored, are always on the edge of your seat. The disadvantage is that the author never really had time to develop the characters. They were this way one moment and another way the next. Virtually no time for narrative that didn't develop the plot.
All in all, it is a barmy story with barmy ideas (see above) but it is an engaging read. If you can overlook it's shortcomings, you will enjoy this book immensely. Me, I don't have a problem with barmy.