There are massive benefits with the dry kit IMO - the trace mix ad macro mix are separate so it's more effective, it's cheaper (your not paying to have heavy water transported), more environmentally friendly and will last longer in storage.
Some people see iron deficiency in their plants when they use all-in-one" fertilisers because the iron reacts with the phosphate and precipitates out of solution becoming unavailable to plants when you add the all-in-one mix to the aquarium water (the pH of the liquid in the bottle is much lower and keeps the iron in solution). To get around this, they then have to add more of the all-in-one mix, making it even less economical.
Mixing the dry ferts takes like 10 minutes, probably about just as long as it would take to go online and order a new bottle of all-in-one, but it lasts longer and you wont be mixing up ferts very often at all, especially for a 19L tank.
All-in-one ferts are OK, and I use them rarely if I'm waiting for a dry salt order to be delivered so pick up a bottle of something with Prime same-day delivery or just from Pets@Home in the meantime, but it annoys me having to do that as they are more expensive and less effective.