nope, never heard of them.
It says they make their own doors. Pretty sure they will be standard slabs of certified chipboard "blanks" that they veneer. I don't know how many factories there are making the chipboard, I wouldn't be surprised if there were only one or two in the country.
The ones I use are made by Premdor but sold under various retailers' names, including Wckes, so you can compare prices. I imagine fancy veneers cost more.
As you may know, veneered doors can be varnished but normally not opiled or waxed. It is said to make the glue holding the varnish, but bering flammable it might also affect the fire rating.
You will also need fire-door linings ("frames") which in softwood are about £30. Veneered or hardwood would cost more. They have grooves machined into them for the intumescent strip you will need. Better ones have the doorstop machined out of the solid, ordinary ones will have loose doorstop strip that is nailed or screwed on. The cheap linings you usually paint white as the colour will not match the door. You should use pink firefoam to seal round the frame and wall.
You can get intumescent strip with furry pile that blocks smoke (and also blocks noise and draughts) but the pile is usually grey or black.
If you haven't had fire doors before, I think you will be very pleased at how much they block noise. They are very heavy and have to be hung on three extra-strong fire-rated hinges, I recommend the lift-off ones which make it easier to take off and replace for maintenance or redecorating. "Hi-Load" is a good brand. Most are zinc-plated and can be painted, stainless are available. Brassed stainless (PVD) are almost unobtainable and very expensive in the firespecification.