No strikes so far from cuttings so they are either hard to strike or don't grow from cuttings at all.
I've heard they are very hard to grow from cuttings
The situation regarding cuttings is like that of Japanese Maples: some varieties/cultivars are very easy to root from cuttings, some are less easy, and others are, for all intents and purposes, 'impossible'. This is what I was told by a grower in Japan. Of my 35 cultivars, 14 can be propagate via cutting while the other 21 must be grafted. I will start testing this myself in Spring 2022.
(The same 'inconsistency' is true of fruit production without the presence of a male: it works well for some, and less well for others; see 7th column here:
http://www.himegaki.jp/about1.html)
I should add that Mr. Yasuhisa Yamaguchi discusses air layers without discriminating among varieties/cultivars. I don't know how we should interpret this silence though.