I just took the ASTB, and also studied from those guides. The math is much easier than the guides but everything else MC, SA,& N/A terms is much harder than the Barrons/Arco guide. I got a 6,6,6 55--which passes for the Marine Corps. I feel like I could do better if i took it again.
On the practice exams, I was missing 3-5 on Math, 3-5 on reading, 1-3 on mechancial comprehension, zero on spatial, and 5-7 on Nautical/aviation. However, on the actual test I know I missed way more than that.
Arco/Barrens do a horrible job of covering avation and nautical terms because they fail to cover specifics. The actual test is much more specific... for example the test might ask you what is the specific task of a "certain" fixed wing aicraft in the navy is--and not the obvious ones like fighter/attack/ or electic warfare. Know the different styles of aircraft parts--for example not just the empennage but the style of empennage not just an elevator but the type of elevator etc...
Hopefully this helps and good luck.