Unity enables shaders to smoothen the transition between LOD meshes (and during culling) and a good balanced approach is to do it with a cutout shader and dithering.

You just have to make the CutoutFragment() look something like this

sampler2D unity_DitherMask;

void CutoutFragment() {

float2 vpos = d.screenPos.xy / d.screenPos.w * _ScreenParams.xy;

vpos /= 4; // the dither mask texture is 4x4
float mask = tex2D(unity_DitherMask, vpos).a;
float sgn = unity_LODFade.x > 0 ? 1.0f : -1.0f;
clip(unity_LODFade.x - mask * sgn);

#if !defined(_NATIVE_A2C)
if (o.Alpha < _Cutoff) {
clip(-1);
}
#endif
}

Code is taken from https://github.com/keijiro/CrossFadingLod and UnityCG.cginc