They are quality are very reputable, I purchased a 55" LG CX C grade for £730 without a stand (which I still think is an utter bargain).
However, be warned it only comes with 3 months warranty for Grade C items and with any electronics there is always a risk. So you have to weight up whether the £400 saving is worthwhile to you. I'm on a budget, so took the risk as 2 months ago the cheapest CX was £1150. It arrived mint with only a small faint scratch roughly 1cm on the screen. You have to be really up close to even notice it.
You should need to hope if there is any fault, it is within the first 3 months.
The none graded items come with 12 months warranty which i assume is just brand new items just open box.
I also purchased a very good condition AirPods Pros for £109, arrived with box, manual, new ear pieces but the charger cases had some blemishes. Saved well over £100 compared to retail.