I like the freedom of choice, that you can choose your rewards. If you want, you buy only buildings or only trains, it's your decision. On the other hand the options are limited, I would prefer a material set. (By the way I would prefer uncommon engines, you seem to unreasonably neglect them ...) I understand this is an electric event, but you just need to give a good set bonus to make a reasonable electric materials set. If you plan to offer a material (uncommon please) set for the next event, you could provide several type of cars so that the players could choose up to 4 types to build their set of choice (I would go for U-235, titanium, marble). This also requires to think over the wagon bundles, because if you offer a lot of material cars in level specific bundles, it will be a big mess. Thank you, keep up the good work 😀