I can second the Disease susceptibility comment. It is a mildew magnet when it's in part shade. Funnily, some people comment that it tolerate shade! However if it is in full Sun and dry climate, it's OK.

Rooting it requires good light, early morning Sun is best if rooting outdoor and misting is likely required if not done in Autumn or early Spring.

The ability to heal with callus is excellent. Chip budding is a pleasure on this understock as the sucess rate is excellent. Roses do not seem to have a lot of vigor on this rootstock. It's suitable to make standard because of the big size, straight cane and medium vigor for the budded roses. Even lateral shoots from a big 2yr basal can be used to make standards because they are simply huge!

I haven't had a powdery mildew problem with this rose and that may be because it gets an extreme case of black spot so that there are no leaves left to get powdery mildew. JMA