I found that skill books added in A21 are bit useless.
Apart from Forge, med, food and explosives, other books are once-off at best.
In fact, I've decided to play with out using any of those and by day 15 I had from loot or tasks: lv4 pistol, lv6 ak, 3 wooden bows (all lv 6), iron crossbow lv 6, iron tools lv 4-6.

This confirmed me that weapon/tools/armor skill books are bit of useless. So I did change it a bit.

This mod will add:
- all gun books will add buff for entity damage 1% -> 35% (lvl 15-100) to respective guns
- all gun books will add buff for reload speed 1% -> 15% (lvl 15-100) to respective guns
- all melle books will add buff for entity damage 1% -> 35% (lvl 15-75) to respective weapons
- all melle books will add buff for stamina reduction 1% -> 15% (lvl 15-75) to respective weapons
- armor books will get phisical damage resist 1% -> 25% (lvl 15-75) to both types of armor
- med books will add passive healing factor 1% -> 1% (lvl 50-75)

Those buffs will stack with skill perks.

Notes:
- robotic books, which unlock baton and junkie/sledge turrets - damage buffs are applied only to batons
- no bonuses for tools/forge/vechicles/electric books (yet?)
- demolition books might get same buffs for rockets but none so far.