The proof is in the pudding. There is little argument that electrolyte drinks may help to prevent dehydration. The idea of "pre-load" is interesting but flawed. The only way this could help is if the user starts in a slightly dehydrated state (which is probably true of most competitors).
Pre-load in medical parlance refers to the amount of blood that comes into the left ventricle and not used in the manner described in the advertisement.
Increasing plasma volume is useful up to a point after which you will just make more pee. Don't get me wrong, it's good and important to pee a lot especially in the heat but it's not like you store the extra plasma volume like a camel as the "hyperhydrated state" implies.
Blood must have a certain level of acidity for the cells of the body to operate optimally. If the blood is too acidic or not acidic enough the cells of the body don't work well. The body has several mechanisms to buffer acidity to maintain a proper balance. The amount of base (or bicarbonate in this case) is likely relatively modest and would likely be buffered by the body's homeostatic system. As the added base is likely to be buffered almost immediately it is unlikely to be of benefit when it is touted to be helpful. Interestingly, this product contains both sodium citrate (which metabolizes to an acid) and sodium bicarbonate (which metabolizes to a base). Net result? Probably zero.
Bottom line: Buy it if it is cheap and you like the taste. Electrolyte drinks help you to stay hydrated and maintain proper balance of salts in your body. The rest of the claims are a lot of bunk and pseudo-science. Sodium citrate provides a nice tang to the drink but it (as well as the sodium bicarbonate) is unlikely to be in sufficient quantities to have the claimed effects (which is probably a good thing since it would wreck your body's own homeostatic systems if it actually made your blood more or less acidic than it should be).