The referral program easily attracts more users towards the site, if it gains good trust in the short. 5% as referral bonus is really big. Some has claimed the referral bonus to be high as 50% and I don't think sites are paying high as that. At the beginning of the service paying 5% is really big and if the 5% is paid based on the wagered volume then it'll be really interesting. 
i believe you are referring to freebitco when you say that some sites offer 50% referal bonus because this is the only gambling site that i know that has a 50% bonus but freebitco did really mean it but that was useless if you cant gather a legit gambler that can wagger huge but a 5% can go a long way if the player that you refer is active but they can be because a crash game is a game that was in favored by many gamblers as when compare to what freebitco games has to offer .