Bought one of these mono laser printers from Ebuyer. Works well and does what’s expected. The refill supplied though isn’t good for 300o pages. Their effectively only partly filled. I guess this  is what happens when you buy a complete system for £40! A quick look at the prices for genuine Samsung replacements gave me a bit of a shock.  So I decided to go the refill root.  Found this company to be extremely efficient and helpful: They sell starter kits that even include a screwdriver, gloves and face mask. But in practice you may care to buy just the standard kits. They cost about £18 , a lot less than a full replacement. Be aware that you can’t refill these indefinately , perhaps 3- 5 times. Also be aware that when refilling you may need to empty the waste as well. Full instructions provided. Do take care though, the toner dust goes every where so don’t wear good clothes or refill on your best carpet.