Custom fit products are tailor-made for your vehicle and therefore fit best.
In comparison, universal products are suitable for almost all vehicles (with certain exceptions).
In general, all products in the XTR line are also custom fit products.
You can recognise a "custom-fit product" by the fact that it is either graphically marked as "custom fit".
Or that the title or description indicates for which vehicle(s) the product is suitable, e.g.:
Seat cover 'Robusto' for Audi A4 year of construction 2017 until today - 2 Seat covers for normal seats