Should I read bonus terms before or after claiming?

Before, because afterwards it is too late to decline. Once a bonus is credited, the wagering, the maximum stake per round, the excluded games and the max cashout all attach to your balance, and cancelling a bonus mid-play sometimes forfeits winnings tied to it. Five figures decide whether an offer is worth taking: the multiplier and whether it applies to bonus alone or deposit plus bonus, the game weightings, the expiry window, the max stake cap, and the cashout cap. Two minutes on the terms page is the entire check. If any of the five is vague or missing, skip the offer.