Guess the description is wrong.
How the crimson weapons work is this.
1) For every 10 levels AFTER 70, you get +5 equip attack. This means that at level 175, you cap out at an extra +50 attack.
2) For every refine up to +15, you gain an additional equip attack bonus that is the square of the refine. So, at +7, it is +49 attack. At +10, it is +100 attack. At +15, which is the cap for this bonus, you get +225 attack.
3) It is a level 3 weapon that gains the normal weapon attack bonus per refine.
4) It is randomly enchanted with an element from any of the following when it is dropped by an enemy: fire, earth, water, wind, shadow, holy, neutral.
You can buy them from others, or you can farm your own -- my suggestion is to get a neutral or holy mace, as those are the most versatile elements.