Hmm, I contemplated that at first but decided against it for some reason that’s not quite clear to me now, but I think I mispredicted its verbosity in both literal and compressed form.

For compression purposes, mine is going to be kinda like this:

  ‹M21 ›5‹H3v1h18›‹M21 ›11‹H3v1h18›‹M21 ›17‹H3v1h18›

Yours will probably treat only one block, slightly bigger, as a repeated thing:

  M21‹ 5H3v1h18›m0‹ 5H3v1h18›m0‹ 5H3v1h18›

I expect that would compress 2–5 bytes smaller.

I’d lowercase that M, too; it doesn’t need to be uppercase, so it might as well be lowercase like the others!

A couple fewer bits or bytes is not going to make a noticeable performance difference.

So? Golfing things like this is mostly about fun, with a side benefit of being aware of things that, on a (much) larger scale, do start to matter.