I've got the original books as well. I think it's cool that there is now an "omnibus" version for all those people who did not have it yet, but I have no idea why they omitted the Tau stuff or the proper procedures for decompression. "They eat your babies" and "make swimming motions with your arms, propelling yourself back aboard the ship" was pure gold.
As with most licensed products (including OW, for what it's worth), bits of it sadly don't add up with GW's own material, but I still recommend it to any fan of the Guard simply for the tone and the grimdark humour. If it uses the same materials and binding as the original Primer and Munitorum Manual, it even feels like something out of the year 1918 … or M41, for that matter.
I find it unfortunate that much of what it says doesn't match up with OW too well - and I'm talking about the non-propaganda parts. The 'average' IG trooper does not pack 6 frag grenades and sufficient charge packs for a few thousand shots.
Welcome to the wonderful world of 40k's "overlapping interpretations", where each book tells you something else.