I have not purchased the same oil radiator as this one, but I happened to have another one with the same characteristics as this one. It is 700 watts with 7 fins, and I can say that it covers a 25 square meter room, with insulation, closed shutters, and double glazed windows, but with the door of the room open. It does a great job, I must say, considering its characteristics (fins/watts/dimensions). Of course, it takes a little longer than a unit with larger characteristics (fins/watts/dimensions) than this one, but it's okay. I have also tried it in an 8 square meter bathroom, and it comfortably heats it up within 20 minutes. In terms of quality, it is sturdy, but oil radiators are generally known to be durable over the years of use. It is also the second most economical heating device with electricity after the air conditioner!
Conclusion: Although this specific oil radiator is intended for a 10 square meter space, it can also function in a larger space of up to 25 square meters, but under the condition that there must be good insulation in the room and no losses from windows and shutters.

I bought it, I put it in my daughter's room... after 30 minutes with the door closed, I enter and it was as if it didn't exist at all.