Very high grade farthing with much lustre, entombed in a CGS slab and graded as CGS78. It's the 'finest known' to CGS/LCGS.
From what I can see, it's certainly a GEF with perhaps the slightest of rub to the breast, knee and shield on the reverse and to the shoulder armour of the king on the obverse. It has a bungled 2nd 'N' in BRITANNIA and really does have delightful lustre in the lower areas. They really don't often come any better than this.
Higher value coins like this are always sent fully insured.