There are a few major problems with this PDF scan. Firstly, I have no idea where pages 4 and 5 are. The e-book jumps from page 3 (the Table of Contents) to page 6. I've never owned a hard copy of the MegaTraveller rulebooks, so I can't say for certain whether the two white pages illustrating the Spinward Marches sector map and the Third Imperium map are what are supposed to appear on pages 4 and 5 or not, but my gut is telling me "No", because the Table of Contents describes page 5 as the "Introduction"... and it looks as though page 6 is just a part of some main section that describes sci-fi roleplaying in more detail. Caveat emptor.
Another problem is the fact that the Spinward Marches map is completely illegible and thus entirely useless. Starport codes on the map are extremely difficult -- if not impossible -- to read and system names are entirely impossible to read. Even the map legend is illegible.
I'm rather disappointed with the scan quality, as the pages are quite obviously not centred and are not scanned at very high resolution to boot. Much of the file size is undoubtedly the little grainy dots on each page (treated as images by the PDF format) that surround all of the printed text; it's pretty much a direct OCR rip from a lossy JPEG scan of the rulebook. If the document were actually remastered, or at least scanned in full 24-bit bitmap with the contrast maximised to make it purely monochrome, I imagine the file size would shrink from 17.7 MB (18.5 MiB) to somewhere in the vicinity of 5 MB or even less. You'll also discover that the angled scans of the pages cause the select tool in Adobe Reader or whatever other PDF reader you use to jump between font sizes, a definite sign of overly permissive OCR.
As for the product itself, I'm feeling as though MegaTraveller is definitely the best version of the Traveller system. The other versions seem to make a habit of dumbing down the bits of the game that make it so much more detailed than other game systems... a real shame. The MegaTraveller storyline does go contrary to the methodology of being able to go anywhere and trade with anyone due to the civil war, but if you don't like that setting you can go ahead and create your own galaxy replete with background, which shouldn't be hard at all given how powerful the planetary generation rules are.
I tend to think of MegaTraveller as a significant spiritual ancestor of GURPS, especially with regards to its Tech Levels which are duplicated almost exactly in every GURPS system. There's even a GURPS Traveller out there which you might also want to pick up.
Finally, be wary of the price. The retail price of the book is, and always has been, $10.00. DriveThruRPG is charging $19.95 and then offering you the $10.00 price as a "discount". This seems a little underhanded to me.