I think it is summed up by looking at the main Vietnam Lonely Planet Guide, they say don't cycle on highway 1 as it is too busy and dangerous. Open the Lonely Planet Cycling Guide and you will see it has 2 long routes that follow this road. We tried it and it was awful.

Definately don't ride the Maekong Delta Meander route it is dangerous and not enjoyable. Maybe some of the other routes are better. The cycling Australia book we have also used and those routes were quite good.

As for the rest of the general issues with the book.
-The maps are too small scale to find things on. Often using 1 map for 2 or 3 days cycling.
-The route notes often miss things like many major junctions and turnings.
-We got lost when the text said go SW and it should have said NW.
-It is not spiral bound and therefore hard to use on a bike.
-The maps are not orientated north south.