Gun should be a selectable option - LaserLyte Trainer Target Steel Tyme Kit

I ordered this for my son who carries a Glock 19. I tried to substitute the smaller training gun for the more comparable, larger model but they wouldn't allow it. I don't understand why as the price, if purchased separately is about the same..I think it's very important that the training incorporate as closely as possible the most similar weapon if possible. There would have been a substantial difference in price overall if the components I wanted were purchased separately. Overall, the accuracy is very good and this is a great training option when trying to save some money as compared to live fire training.