Like many middle-aged people I read this at school 30+ years ago and have a well-worn paperback copy acquired in early adulthood. With that copy on the verge of disintegration, it's reassuring to renew. I would hate to be unable to re-read this at least once a year! As with most of Heinlein's "juveniles" from the 1950's its a smoothly engineered story line with key background themes beautifully & economically sketched. Also typical: coming of age topics; a rather romantic view of warfare (or is it?); future technology seen through a mid 20th century lens; and a rushed ending ... though this one is much more satisfactory than some Heinlein endings. The best of Heinlein is very much present in terms of convincing atmosphere. Finally, Heinlein is entirely capable of putting a foot wrong with narrative drive, human characterization, or aliens - he falls into none of those (by his own towering standards) traps here. But, indeed, why no Kindle edition? Missed opportunity as I strongly suspect many people, like me, would buy both formats "for old time's sake" combined with convenience when traveling. Travis Taylor's Afterword is amusing and thought-provoking. Well done the publisher for bothering to add value this way.