There's a massive amount of reading in this collection, and it's a tribute to the author's range of imagination and productivity. He covers a lot of ground - The Para-Time police (amongst my favourites) have their adventures in a vast range of alternate Earth's, whist Galactic Emperors decide on the fate of entire planets, and interstellar travellers deal with aliens of all kinds. There is even at least one straightforward, non-SF murder mystery.
Perhaps inevitably, certain common themes start to show themselves over all the stories. Piper, it would seem, likes the idea of strong governments who deal firmly with lawbreakers. His heroes are uncompromising men of action, firm and decisive, who have no problems with self doubt. Even if it means dropping a nuclear bomb on an alien city!
Less seriously, his characters all smoke incessantly. Even the Emperor of the Galaxy, thousands of years in the future, finishes breakfast with a cup of coffee and a cigarette! Mankind in Piper's future have developed interstellar travel without realising the health hazard of inhaling nicotine.
But it's probably unfair to make too much of it. Probably most of us are guilty of some degree of cultural blindness, and even if the characters are all essential mid-century Americans, they do have exciting lives in exotic locations - and that's what the stories convey most. They are adventures, and they rattle along at a good enough speed so that you can get past the anachronisms without too much pain.
This is classic Science Fiction from the Golden Age, and for the price, a real bargain!