Not cheap but will last forever!
Their products do not have a vitreous enamel coating. The frying pans might be very good, since they can be seasoned instead, but I suspect they would not be very good casseroles: acidic sauces would react with the iron and taint the dish, they would probably inevitably rust (and so not last very long, never mind ‘forever’), and the wooden knobs would probably not survive prolonged use in an oven.
With regard to those commenting on whether weight of the casserole is or is not an issue for them or their spouse/partner, to state the bleeding obvious casseroles come in a large range of sizes, and the weights of different sizes when full undoubtedly vary hugely. It’s meaningless to say that the weight is or is not a problem for you, without stating the actual approximate weight of your full casserole (and its size, which will limit the weight).
As to the quality or otherwise of the copies made by the likes of Ikea and Sainsbury’s, they are relatively simple products, so I would have expected that providing there is generally good basic quality control in the manufacturing process (quality of iron and pour [no imperfections/large air bubbles], reasonable thickness of iron, good enamel coating), then they should last as long as – and perform as well as – Le Creuset. It may not be possible to judge the manufacturing QC of a copy just by looking at the finished article in the shop, but if it fails quickly due to a defect, you should be able to return it to retailers like Ikea.