Choosing between the two I would definitely go for the 33 over the 100 Ltr. Early on that 33 liter will last you about 10 days between res changes, later a really big plant would need a res change about every 3 days.
You would probably use that kit about one or two grows and then buy an air pump the cost just as much. But that's kind of the way it is with most kits you buy to learn and then you figure out what you really need and replace everything.
In my part of the world it's very easy to get all the components of a kit and assemble them yourself. Here are some of the items that I have used in my deep water culture growing days.
So as you see, you have a net pot it just sits down on top of your bucket and then you drop your airline down through the net pot. You can use any size bucket you would want with that kind of setup. I like bigger air pumps even if I'm only running one or two buckets.
You can drill a hole down at the bottom of the buckets and use bulkhead seals to join more than one bucket together so you can have one bucket under a scrog and one bucket out from under a scrog. What that allows you to do is leave a big plant for up to a week with the same res and change your res without moving your plants around.
To change a reservoir on a single bucket system you just make up a complete brand new bucket of nutrients pick that net pot up and set it down in the new nutrients and you're good to go. You already have your airline down in through there your stone is down where your roots are, it all transfers really easy.
It's about 7 a.m. here and I'm already Totally Baked on some blue dream wax so I don't know how much sense this makes.