Patter summary (in case those links threw you into a where's-my-big-red-pen tailspin): Both foundations retail for £44 for a 35ml squeeze-tube and are imbued with "the futuristic I.M.C® Technology (Intensive Mimetic Camouflage)," hyaluronic acid and other unspecified "regenerating active ingredients." Both promise a 'velvet' matte-yet-light-diffusing finish with shine control and moisturisation suitable for all skintypes. Cover Expert offers more coverage.
My first impressions: the scent is very strong and very sweet rose with a hefty dose of powder. (If you're familiar with the ByTerry line, it is the powdery roses of the Blush Velouté rather than the cleaner tea roses of the skincare.) Both foundations had a great deal of silicone-y slip and texture-wise are somewhere between Armani Face Fabric foundations and Becca Beach Tints; both set completely matte on my dry skin.
I can't comment further because the shade range starts off too dark -- much darker than that of the recently-discontinued Lumiere Veloutée, which provided my only near-match in the line.
Left to Right:
Chantecaille Future Skin Porcelain (as a reference, because Chante was the next counter over)
The rest are all ByTerry:
Cover Expert 1 Fair Beige
Cover Expert 2 Neutral Beige
Sheer Expert 1 Fair Beige
Sheer Expert 2 Neutral Beige
Teint Délectation 1 Milky Vanilla
Touche Veloutée concealer pen 1 Porcelain
Light Expert foundation brush 101 Beige Light
Light Expert foundation brush 1 Rosy Light