Tom Morris was apparently surprised when I asked for 7 strands the last time I ordered lines from him, because he emailed me to confirm that.
The 19 strands are soft, supple and all, but most the guys I fly with were put off them by the likelihood of individual strand failure, since the wire strands are so much smaller, and we were flying off hard surfaces.
I think IF I flew off a good grass field, I'd be less worried about that and more likely to use 19 strands, so opinions vary on that. There is, of course, a variation of grass quality. Mark flies on part of a grass strip airport...probably not as lush as a soccer field like we will probably be flying on next year.
I flew with some 19 strands for a season or two and didn't really have any problems with them, but went to 7 strands anyway, 'cause line trouble is pretty deadly if you don't catch it in time, especially over pavement with pretty expensive (to me) engines that may be hard to replace.

Steve