In DH 2014 every time a new region is released you can start the series hunts with the rifle of the previous region. After hunt 8/9 or 9/20, the hunter lady who uses to wear clothes (specially tops and bras) three sizes smaller than the ones she uses when finishes what she does for a living and returns home) offers you an OTO for the gold rifle. Then you have to decide whether to accept the OTO and buy the gold rifle, or not and in such a case you have to buy the Hunter Bucks rifle and can decently complete the series.
However, in Dino you are forced to have the series weapon, whatever it is, (both in the series hunts and in the trophy hunts) to start playing. So you are forced to buy either the gold or the HB weapon from moment 1. When you are about to complete the series you get the OTO. But at that moment either you already have the gold weapon or if you bought the HB weapon and there are only a few hunts left in the series that you can complete with it, you do not need the gold weapon.
If you are an Androider (or an iOSer who buys game gold with real bucks), you have deep gold pockets and can buy the gold weapons from the beginning. You do not need OTOs. If you are an average iOSer (those who do not buy game gold -a vast majority, I tend to believe-) you always run short of gold, so if you have already bought the HB weapon and have almost completed the series, how are you supposed to spend your little treasury in weapons that you do not need?
Sorry, but I do not find the logics behind the OTOs in Dino.