A ₦10,000 free bet is not worth ₦10,000. Most bonuses are stake-not-returned, so the real value is the profit at the price you take — not the headline number.
The free stake is not yours. If you win, the book pays the profit only and removes the free stake. So a ₦5,000 free bet at 3.00 returns ₦10,000 profit, not ₦15,000.
Pick a price around 2.00 to 4.00. Extremely short prices waste the bonus and very long prices reduce its expected value. Compare the rollover terms before you claim anything.