You're not missing anything at all. This has been commented on before. A friend of mine bought cheap inkjet printers, they were on special at £29.99 I think it was. 2 replacement cartridges were about £40 at the time. Since it was cheaper to buy a new printer he bought ten of them. I personally think he was rather stupid doing this as he could have bought a cheap Epson at £40 then bought a pair of compatibles for about £5 each and this would have been cheaper but I didn't mention it to him at the time as he thought he had got a great bargain and I didn't want to dissapoint him. Perhaps you might try and see if reconditioned toner drums are cheaper.
I currently refill my B&W Samsung Toner (from a different supplier). And was thinking of getting the colour laser. But even at £112.50 for the full set in your link, it's nearly as expensive as buying the printer.
Remembering that most new printers come with what they euphemistically refer to as a "Low user cartridge" i.e. it's only part full. I have however been guilty of using Dell 720s as semi disposables, offer price £9.99 inc carr, I bought two and some bottles of refill ink, when the cartridges give up, the printer will be binned as getting new cartridges isn't cost effective.
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