Haven't had any experience using them with sheep, but we certainly do take them into account when buying bulls and bull semen.
If they were widely used in Texel-land, I'd be urging BH to take note of them. Small lambs at birthing and fast growth rates is what I want! Not these socking great tanks of lambs - they're all very impressive, maybe, but it wears their mothers out carrying the two of them around for the last few weeks.