Personally, I avoid the aquarium kits as they tend to be a lot more expensive than just building your own kit, plus they're less flexible in terms of how you set them up.
As for the puffers: definitely highly recommended! The thing about their beaks is actually a myth, though. Lots of larger puffer species *do* need to eat hard foods in order to wear down their beaks, but dwarf puffers don't have the ever-growing beaks of their larger cousins. So, you don't need to worry about finding them extra tiny snails that they can crush or anything like that. With dwarf puffers, it's just a matter of finding a steady source of foods they'll actually eat. Sometimes they can be stubborn about eating even frozen foods, but I've never encountered dwarf puffers that wouldn't eat live blackworms and live snails. Pond snails are extremely easy to breed. Just go to any local pet shop and they probably have an infestation of them somewhere and will gladly give you some for free. Then, you can just put them in any other established tank you've got and they should start breeding like crazy. Until you have your own breeding colony you may have to rely on live worms or snails from the pet shop.
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